In a mixing bowl, combine ground beef, salt, black pepper, garlic powder, and onion powder. Mix gently until just combined, then form into 4 equal patties.

Cook the Patties

Heat a skillet or grill over medium-high heat. Cook the patties for about 4-5 minutes on each side, or until they reach your desired doneness. Remove from heat and let them rest.

Gravy Preparation

Sauté the Vegetables

In a saucepan, melt butter over medium heat. Add the sliced mushrooms and diced onion, sauté until the mushrooms are browned and the onions are translucent, about 5-7 minutes.

Make the Roux

Sprinkle flour over the sautéed mushrooms and onions. Stir well to combine and cook for about 1-2 minutes until the flour is lightly toasted.

Add Broth

Gradually whisk in the beef broth, ensuring there are no lumps. Bring to a simmer and cook until the gravy thickens, about 5-10 minutes. Stir in Worcestershire sauce, salt, and pepper.

Assembly

Toast the Bread

While the gravy simmers, toast the thick cut wheatberry bread slices until golden brown.

Assemble the Burger

Place each burger patty on a slice of toasted wheatberry bread. Ladle generous amounts of the mushroom and onion gravy over each patty. Serve immediately.