Consider this a mash-up of two comfort food classics — French onion soup and a beef dip sandwich. With the right treatment, an affordable sirloin tip gets transformed into a juicy, tender cut that is the perfect pair for caramelized onions, melted gruyere cheese and a luxe French onion jus. Make sure not to skip the horseradish mayo, it offers some much-needed brightness to cut through all the richness.
ingredients
French Onion Jus
Roast Beef
Horseradish-Mayo Spread
Sandwich assembly
directions
Remove beef from fridge and bring to room temperature for 1 hour.
To make the French onion jus, heat oil and butter in a large pot over medium heat. Add sliced onions, season with salt and pepper and cook, stirring frequently, until onions reduce in volume by about ⅓ and begin to soften, 8 minutes.
Reduce heat to low and cook, stirring occasionally, until onions are deep brown and jammy, 1 – 1 ½ hours. If onions begin to stick to the bottom of the pot or seem at risk of burning, add a few tablespoons of water and scrape up any brown bits and continue cooking. Add sherry or wine and cook until liquid is mostly evaporated, about 3 minutes. Remove about half of the caramelized onions from the pot and reserve for later.
Slowly pour in beef broth and stir in Worcestershire, beef bouillon cubes and thyme sprigs. Bring to a boil, reduce heat to low and simmer until thickened slightly, 30 minutes. Remove thyme sprigs and stir in sherry vinegar. Taste, and season with more salt, if needed.
Meanwhile, prepare the roast beef. Preheat oven to 450°F. In a small food processor or blender, add the butter, chopped herbs, garlic, salt and pepper. Blitz together until well combined and smooth. Pat the meat dry with paper towels and arrange on top of onion slices in a medium baking dish.
Spread butter mixture all over the meat to evenly coat. Sprinkle generously with salt and pepper all over.
Transfer beef to the middle rack of the oven and roast at 450°F for 15 minutes. Reduce heat to 300°F, and continue to roast until cooked through and the internal temperature of the thickest part of the meat registers 130°F-140°F for medium-rare, 15-20 minutes per pound. The meat will continue to cook once removed from the oven, so aim for a few degrees below the target temperature. Allow to rest for at least 20 minutes before slicing. Roast beef can be made a day ahead.
To make the horseradish-mayo spread, stir together mayonnaise, horseradish, chives, mustard, lemon juice, and salt in a medium bowl to combine.
Slice roast beef with a sharp knife into very thin slices, working against the grain of the meat.
Slice each bun in half lengthwise and arrange on a large baking sheet (you may need to work in batches). Spread both pieces of bread with horseradish mayonnaise spread. Divide meat and caramelized onions among buns and top with thin slices of gruyere.
Transfer to oven and broil until cheese is just melted and buns are lightly toasted, 3-5 minutes.
Serve sandwiches with a side of French onion jus for dipping.
