4 hamburger buns
1/2 tsp. cornstarch
1 1/2 tbsp. Worcestershire sauce
1 1/2 tbsp. cider or red wine vinegar
1/3 cup ketchup
1/4 cup tomato paste
1 tsp. kosher salt
1/2 tsp. dry mustard
1/4 tsp. red pepper flakes
2 tsp. paprika
1 tbsp. brown sugar
2 cloves garlic
1/2 yellow onion diced
1 tbsp. unsalted butter
1 tbsp. olive or vegetable oil
1/2 tsp. baking soda
2 tbsp. water
1 pound 85% lean ground beef