Ingredients
1 large egg
3/4 cup ketchup
1 medium onion, peeled and roughly chopped
1 rib celery, roughly chopped
1 carrot, peeled and roughly chopped
1 pound ground beef (85 percent lean)
1 pound ground pork
1 1/2 cups panko breadcrumbs
1 tablespoon dried mustard
2 tablespoons Worcestershire sauce
1/4 cup packed finely chopped mixed herbs, such as parsley, thyme, and sage
Kosher salt and freshly ground pepper
Brioche buns, green-leaf lettuce, mayonnaise, and sliced pickles, for serving
Preparation
Preheat oven to 375 degrees. In a large bowl, whisk together egg and 1/4 cup ketchup.
In a food processor, pulse onion, celery, and carrot until finely minced, scraping down sides of bowl to ensure even chopping. Add vegetables to ketchup mixture, along with meat, panko, mustard, Worcestershire, herbs,2 1/2 teaspoons salt, and 1/2 teaspoon pepper. Mix well with your hands until thoroughly combined.
On a rimmed baking sheet lined with parchment, firmly pat mixture into a long, narrow loaf (4 by 12 by 1 1/2 inches). Coat top and sides with remaining 1/2 cup ketchup. Bake until browned and a thermometer inserted into thickest part reaches 165 degrees, 45 to 55 minutes. Let cool at least 30 minutes, then cut into thick slices. Serve on buns, with lettuce, mayonnaise, and pickles.
