Peppercorn Roast Beef with Onion Gravy

Name: Peppercorn Roast Beef with Onion Gravy
Ingredients: 1 top sirloin roast, about 4 pounds (1.8 kilograms); 4 yellow onions, thinly sliced; 1 tablespoon olive oil; Kosher salt and freshly ground black pepper; 1/4 cup (57 grams) unsalted butter, at room temperature; 2 tablespoons cracked black pepper; 1 tablespoon finely chopped rosemary; 1/2 teaspoon garlic powder; 3 tablespoons all-purpose flour; 2 tablespoons (30 milliliters) brandy, white wine or red wine, optional; 2 1/2 to 3 cups (625 to 750 milliliters) low-sodium beef stock; Prepared horseradish, for serving