How to Make It
Melt the butter in a large skillet. When the foam subsides, add the diced baguette in an even layer. Cook over moderate heat until browned on the bottom, about 3 minutes. Stir and cook until evenly browned and crisp, about 2 minutes longer. Transfer to a plate.
Cook the egg in boiling water for 2 1/2 minutes; drain, then scoop the egg out of the shell into a blender. Add 6 of the anchovies, the lemon juice, vinegar, garlic, 1 teaspoon of mustard and 1 teaspoon of the Worcestershire sauce. Slowly add the olive oil and blend at medium-low speed until it is incorporated and the mixture is creamy. Pour the dressing into a small bowl and season with salt and pepper.
In a food processor, finely chop the 4 remaining anchovies with the onion, capers, parsley and horseradish. Transfer to a large mixing bowl. Add the remaining 1 tablespoon of mustard, 2 teaspoons of Worcestershire sauce, the hot sauce and ground beef and mix well. Form the meat into 12 patties and season them with salt and pepper.
Heat 1 teaspoon of the canola oil in a large, heavy skillet. Add 6 of the burgers and cook over high heat for about 1 minute on each side for rare, and about 30 seconds longer on each side for medium rare. Transfer to a plate. Repeat with the remaining 1 teaspoon of canola oil and 6 burgers.
In a large bowl, combine the romaine lettuce with 1/2 cup of the dressing and the croutons and toss to coat. Mound the salad on plates and set 3 burgers on each salad. Drizzle the remaining dressing over the salads and serve.