Preheat oven to 400°F.

Heat the olive oil in a medium skillet over high heat. When oil is hot, add the red onion. Cook, stirring occasionally, until the onion is soft and golden, about 5 minutes. Set aside.

Remove crusts from bread, and place slices in the bowl of a food processor. Process until crumbs form, about 10 seconds. Put in large mixing bowl.

Place carrot, celery, onion, and garlic in the food processor and process until vegetables have been minced, about 30 seconds, stopping to scrape down the sides of the bowl, if needed. Transfer the vegetables to the bowl with the bread crumbs.

Add ½ cup ketchup, 2 teaspoons Dijon mustard, ground beef and pork, eggs, salt, pepper, Tabasco, and rosemary. Use your hands to mix everything together.

Set a wire baking rack into cookie sheet. Cut a 5x11 piece of parchment paper, and place over the center of the rack to prevent the meatloaf from falling through. Form an elongated loaf covering the parchment.

Mix the remaining ketchup, mustard, and the brown sugar in a bowl, then spread on the meat. Spread the reserved sautéed onion on top of the meat.

Bake 30 minutes, then sprinkle the rosemary needles on top. Continue baking until a meat thermometer registers 160°F, about 25 minutes more. Let meatloaf cool on the rack for 15 minutes before slicing.