Step 1

Preheat an oven to 400 degrees F (200 degrees C).

Step 2

Melt the butter in a skillet over low heat. Cook and stir until the onion has softened and turned translucent, 10 to 15 minutes. Meanwhile, place the bacon in a large, deep skillet, and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on a paper towel-lined plate. Cut bacon into bite-sized pieces and set aside.

Step 3

Combine the baked beans, Worcestershire sauce, ketchup, mustard, and onions in a 2-quart casserole dish. Stir in 2/3 of the cooked bacon and 1/4 of the brown sugar until evenly mixed. Cover the bean mixture with the remaining bacon, and sprinkle with the remaining brown sugar.

Step 4

Bake in the preheated oven until hot and bubbly, about 45 minutes.