Thinly sliced roast beef layered with sweet caramelized onions and sharp horseradish cream on toasted bread—a bold, savory sandwich with tangy bite.
Caramelizing onions low and slow (25–30 minutes) develops deep sweetness that balances horseradish's sharpness; do not rush this step. Fresh horseradish root has significantly more bite than prepared horseradish; start with 2 oz if sensitive to heat and adjust to taste.
Horseradish cream can be made up to 2 hours ahead; cover and refrigerate until assembly. If using prepared horseradish, reduce sour cream to ¼ cup and omit Dijon mustard, then taste and adjust seasoning.
Ingredients
Scale
Measurement units
- 3 medium yellow onions
- 3 tbsp butter (3 tablespoons plus 2 tablespoons, divided)
- salt (to taste)
- black pepper (to taste)
- 3 oz fresh horseradish root (or 4 tbsp prepared horseradish if fresh unavailable)
- ½ cup sour cream
- 1 tbsp Dijon mustard
- 1 lb roast beef (deli-counter or freshly sliced)
- 8 slices sturdy bread (sourdough, rye, or ciabatta)
- 2 tbsp butter for toasting (for bread)
Ingredients
Scale
Measurement units
- 3 medium yellow onions
- 3 tbsp butter (3 tablespoons plus 2 tablespoons, divided)
- salt (to taste)
- black pepper (to taste)
- 3 oz fresh horseradish root (or 4 tbsp prepared horseradish if fresh unavailable)
- ½ cup sour cream
- 1 tbsp Dijon mustard
- 1 lb roast beef (deli-counter or freshly sliced)
- 8 slices sturdy bread (sourdough, rye, or ciabatta)
- 2 tbsp butter for toasting (for bread)
Instructions
Caramelize the onions
Melt butter (3 tablespoon) in a large skillet over medium-low heat.
Add the sliced onions and a pinch of salt; stir to coat evenly.
Cook, stirring occasionally, until onions are deep golden brown and very soft, 25–30 minutes. Do not rush; low heat develops sweetness.
Season with salt and black pepper to taste. Transfer to a plate and set aside.
Equipment: large skillet or sauté pan, toaster or skillet
Prepare the horseradish cream
Finely grate the fresh horseradish root (3 ounce) using a microplane or box grater into a small bowl.
Stir in sour cream (½ cup) and Dijon mustard (1 tablespoon) until smooth and well combined.
Taste and adjust seasoning with salt and black pepper as needed.
Equipment: microplane or box grater, small bowl
Toast the bread
butter (2 tablespoon) one side of each of the 8 bread slices lightly with butter (2 tablespoon) total.
Toast in a toaster or skillet over medium heat, butter (2 tablespoon)-side down, until golden and crisp, 2–3 minutes per side.
Equipment: toaster or skillet, large skillet or sauté pan
Assemble the sandwiches
Lay 4 toasted bread slices on a work surface, toasted-side up.
Spread 2 tbsp horseradish cream on each of the 4 slices.
Layer 4 oz thinly sliced roast beef (1 lb) on each slice, dividing evenly.
Top each with a quarter of the caramelized onions.
Crown each sandwich with a second toasted bread slice, toasted-side down, and press gently.
Cut diagonally and serve immediately.
Before you cook
Cook notes
- • Caramelizing onions low and slow (25–30 minutes) develops deep sweetness that balances horseradish's sharpness; do not rush this step.
- • Fresh horseradish root has significantly more bite than prepared horseradish; start with 2 oz if sensitive to heat and adjust to taste.
- • Horseradish cream can be made up to 2 hours ahead; cover and refrigerate until assembly.
- • If using prepared horseradish, reduce sour cream to ¼ cup and omit Dijon mustard, then taste and adjust seasoning.
- • Roast beef should be sliced thin enough to drape; ask the deli counter for shaved or thin-sliced cuts.
- • Toast bread just before assembly to keep it crisp and warm.
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