Place ground brisket and ground pork (if using) in a large bowl. Add salt, black pepper, garlic powder, onion powder, and Worcestershire sauce. Gently combine with your hands or a spatula until just mixed — avoid overworking. Divide into two equal portions and form each into a patty about 3/4-inch thick and slightly wider than the buns (they will shrink as they cook). Make a shallow dimple in the center of each patty with your thumb to promote even cooking.

Cook the patties

Heat a cast-iron skillet or heavy-bottomed pan over medium-high heat and add the neutral oil. When the oil shimmers, add patties. Cook undisturbed 3-4 minutes until a deep brown crust forms. Flip and reduce heat to medium. Add a slice of cheese to each patty during the last 1-2 minutes of cooking and cover the pan or place a lid to help cheese melt. Cook to an internal temperature of 160°F (71°C) for medium-well (brisket benefits from well-done to render fat) or to your preferred doneness. Remove patties and rest 3-5 minutes.

Blueberry-Onion Jam

Sauté onion

While the patties rest (or before cooking patties), heat a small saucepan over medium heat and add butter or olive oil. Add the finely chopped onion and sauté until very soft and translucent, about 6-8 minutes, stirring occasionally. If onions begin to brown too much, reduce heat.

Simmer blueberries

Add the blueberries, brown sugar, and a pinch of salt to the softened onions. Stir to combine, then bring to a gentle simmer. Cook, stirring occasionally, until the berries break down and the mixture thickens to a jammy consistency, about 8-10 minutes. If you prefer a smoother jam, lightly mash berries with a spoon or potato masher as they cook.

Finish jam

Stir in balsamic vinegar, lemon juice, black pepper, and red pepper flakes (if using). Taste and adjust seasoning with a little more salt or balsamic as needed. Remove from heat and keep warm until assembly. The jam will thicken further as it cools.

Assembly & Toppings

Toast buns

Spread butter on the cut sides of the buns. Toast in a hot dry skillet or on a griddle until golden and crisp, about 1-2 minutes per side. Alternatively, toast under a broiler for 1-2 minutes, watching closely.

Prepare sauce

In a small bowl, combine mayonnaise and Dijon mustard. Taste and add a pinch of salt if desired. This provides a creamy counterpoint to the sweet-tart blueberry jam.

Assemble burgers

Spread about 1 tablespoon of the mayo-Dijon sauce on the bottom bun. Place a handful (about 1/2 cup) of arugula or baby greens on the sauce to keep the bun from getting soggy. Set the rested, cheese-topped brisket patty on the greens. Spoon 2-3 tablespoons of the warm blueberry-onion jam over the patty. Top with the other bun half and press gently. Serve immediately.