Ultimate Open-Faced Roast Beef Sandwich with Sweet Caramelized Onions and Zesty Horseradish Aioli
Few dishes can rival the comfort and satisfaction of a perfectly crafted open-faced sandwich. This Open-Faced Roast Beef Sandwich with Caramelized Onions and Horseradish Aioli elevates a classic deli favorite into a gourmet experience. Tender, thinly sliced roast beef is nestled atop crusty ciabatta bread, crowned with rich, golden caramelized onions and a bold, creamy horseradish aioli that adds just the right amount of zing. Whether you’re hosting a casual lunch, preparing a hearty dinner, or looking to impress guests with a sophisticated yet approachable dish, this sandwich is a showstopper. The combination of textures—crisp bread, succulent beef, velvety onions, and creamy aioli—creates a harmony of flavors that will leave everyone craving seconds.
This recipe is designed to serve 4, but you can easily scale it up or down depending on your needs. Let’s dive into the details of crafting this mouthwatering creation, complete with tips for customization and serving suggestions to make it your own.
Ingredients
For the Sandwich:
- 1 large loaf of ciabatta bread (about 12–16 inches long), halved lengthwise for an open-faced presentation
- ¾ lb thinly sliced roast beef (medium-rare for optimal tenderness and flavor; ask your butcher for deli-style slices)
- 2 tbsp extra-virgin olive oil (for brushing the bread before toasting)
- 3 tbsp fresh parsley, finely chopped (for a vibrant, fresh garnish)
- Optional: A handful of baby arugula or microgreens for a peppery, fresh topping
For the Caramelized Onions:
- 3 medium yellow onions (or sweet onions like Vidalia for extra sweetness), thinly sliced into half-moons
- 2½ tbsp unsalted butter (for richness and to promote browning)
- 1½ tbsp extra-virgin olive oil (to prevent the butter from burning)
- 1 heaping tsp granulated sugar (to enhance the onions’ natural sweetness)
- ¼ tsp kosher salt (to draw out moisture and season the onions)
- 1 tbsp balsamic vinegar (optional, for a touch of tangy depth)
For the Horseradish Aioli:
- ¾ cup high-quality mayonnaise (use a brand you love or make your own for extra flair)
- 1½ tbsp prepared horseradish (adjust to taste for more or less heat)
- 1½ tsp fresh lemon juice (for brightness and balance)
- 1 large garlic clove, minced or grated (for a subtle, savory kick)
- ¼ tsp kosher salt (or to taste)
- ⅛ tsp freshly ground black pepper (for a hint of spice)
- Optional: 1 tsp Dijon mustard for added complexity
Instructions
Step 1: Craft the Caramelized Onions
Caramelized onions are the heart and soul of this sandwich, bringing a sweet, savory depth that complements the roast beef perfectly. While they take time, the process is simple and well worth the effort.
- Prepare the onions: Peel and thinly slice the onions into half-moons for even cooking. Aim for slices about ⅛-inch thick to ensure they caramelize evenly.
- Heat the pan: In a large, heavy-bottomed skillet (cast iron works wonderfully), melt the butter with the olive oil over medium-low heat. The oil helps prevent the butter from burning during the long cooking process.
- Cook the onions: Add the sliced onions to the skillet along with a pinch of kosher salt. Stir to coat the onions in the butter-oil mixture. Cook slowly, stirring every 5–7 minutes, for 35–45 minutes. The onions will soften, then gradually turn golden and develop a rich, caramel-brown hue. Be patient—low and slow is the key to perfect caramelization.
- Add sugar and optional vinegar: In the final 10 minutes of cooking, sprinkle the sugar over the onions to enhance their sweetness. If desired, add the balsamic vinegar for a subtle tangy note. Stir well and cook until the onions are deeply golden and jammy. Set aside, keeping them warm if possible.
Pro Tip: Make the onions a day ahead and store them in an airtight container in the refrigerator. Reheat gently before assembling the sandwiches.
Step 2: Whip Up the Horseradish Aioli
The horseradish aioli is the bold, creamy counterpart to the sweet onions and savory beef. It’s quick to make and can be adjusted to suit your taste.
- Combine ingredients: In a medium bowl, whisk together the mayonnaise, prepared horseradish, lemon juice, minced garlic, salt, and black pepper. If using Dijon mustard, add it here for an extra layer of flavor.
- Taste and adjust: Sample the aioli and adjust the horseradish for more heat or lemon juice for brightness, if needed. The aioli should be bold yet balanced, with a creamy texture and a zesty kick.
- Chill: Cover the bowl with plastic wrap and refrigerate the aioli for at least 15 minutes to let the flavors meld. This can be made up to 2 days in advance.
Pro Tip: For a smoother aioli, use a microplane to grate the garlic, ensuring it blends seamlessly into the mixture.
Step 3: Toast the Ciabatta
The crusty, chewy texture of ciabatta is ideal for an open-faced sandwich, providing a sturdy base that holds up to the toppings without becoming soggy.
- Slice the bread: Cut the ciabatta loaf in half lengthwise, then into four equal portions (about 4–5 inches each) for individual servings.
- Brush with oil: Lightly brush the cut side of each piece with olive oil to enhance flavor and promote crispiness.
- Toast the bread: Heat a large skillet or griddle over medium heat and place the bread cut-side down. Toast for 2–3 minutes until golden and crisp. Alternatively, place the bread cut-side up on a baking sheet and broil in the oven for 1–2 minutes, watching closely to avoid burning.
Pro Tip: For extra flavor, rub the toasted bread with a halved garlic clove while still warm for a subtle, aromatic boost.
Step 4: Assemble the Sandwiches
Now comes the fun part—building your masterpiece!
- Spread the aioli: Generously slather the horseradish aioli over the toasted side of each ciabatta piece. Don’t skimp—this is where the flavor shines!
- Layer the roast beef: Arrange the thinly sliced roast beef evenly over the aioli, folding or draping the slices for an appealing presentation. If the beef is cold, warm it slightly in a skillet or microwave to enhance its flavor and texture.
- Add the onions: Spoon a generous portion of warm caramelized onions over the roast beef, spreading them evenly to ensure every bite is packed with flavor.
- Garnish: Sprinkle the chopped parsley over the top for a pop of color and freshness. If using arugula or microgreens, add a small handful for a peppery contrast.
Step 5: Serve and Enjoy
Present the sandwiches open-faced, with the toppings proudly displayed. For a rustic touch, serve each portion with the top half of the ciabatta slightly askew or on the side, allowing diners to admire the layers. These sandwiches are best enjoyed warm or at room temperature, paired with a simple side salad, crispy fries, or homemade potato chips.
Serving Suggestions:
- Pair with a side: Try a crisp green salad with a light vinaigrette, roasted root vegetables, or a tangy coleslaw to complement the rich flavors.
- Beverage pairings: A chilled glass of sauvignon blanc, a hoppy IPA, or a sparkling water with lemon enhances the meal’s bold flavors.
- Make it a meal: Add a pickle spear or a few cornichons on the side for a classic deli vibe.
Customization Ideas
This recipe is versatile and can be tailored to suit your preferences or dietary needs:
- Bread Swap: If ciabatta isn’t available, try a sourdough boule, a French baguette, or a hearty rye loaf for a different flavor profile.
- Cheese Option: For an indulgent twist, add a slice of melted provolone, sharp cheddar, or creamy brie before topping with the onions.
- Vegetarian Version: Replace the roast beef with grilled portobello mushrooms or roasted eggplant slices for a meatless alternative.
- Spice it Up: Add a pinch of cayenne or smoked paprika to the aioli for a smoky, spicy kick.
Storage and Make-Ahead Tips
- Caramelized Onions: Store in an airtight container in the fridge for up to 5 days or freeze for up to 3 months. Reheat gently before using.
- Horseradish Aioli: Keeps in the refrigerator for up to 5 days. Stir well before serving.
- Assembled Sandwiches: These are best enjoyed fresh, but you can prep the components ahead and assemble just before serving to maintain the bread’s crispness.
Why You’ll Love This Recipe
This open-faced roast beef sandwich is a celebration of bold, comforting flavors. The caramelized onions bring a sweet, melt-in-your-mouth richness, while the horseradish aioli adds a creamy, zesty punch that cuts through the savory beef. The toasted ciabatta provides the perfect crunchy base, making every bite a delightful mix of textures and tastes. Whether you’re serving it for a cozy weeknight dinner or a casual gathering with friends, this sandwich is sure to impress.
Ready to elevate your sandwich game? Try this recipe and share your creations with us in the comments below! What’s your favorite way to customize an open-faced sandwich?
