Step 1

Preheat oven to 350˚F. Cook bacon in a large saucepan over medium, stirring often, until mostly crisp, 8 to 10 minutes. Remove bacon from pan using a slotted spoon, and transfer to a plate lined with paper towels; set aside. Reserve 1 tablespoon drippings in pan.

Step 2

While bacon cooks, place beef, mustard, salt, 1 tablespoon of the vinegar, and ¾ teaspoon of the pepper in an 11- x 7-inch baking dish. Mix using your hands until well combined. Press mixture into an even layer. Bake in preheated oven until browned (meat will not be fully cooked), 10 to 12 minutes. Remove from oven; let stand 5 minutes. (Keep oven on.)

Step 3

Meanwhile, add onion to reserved drippings in pan; cook over medium, stirring occasionally, until tender, about 5 minutes. Remove pan from heat. Transfer bacon to a cutting board; finely chop.

Step 4

Using a long spatula, transfer beef patty from baking dish to a baking sheet lined with paper towels to drain. Wipe dish clean; coat with cooking spray.

Step 5

Add bacon, sugar, and remaining ¼ cup vinegar to onion in pan. Bring to a boil over high, stirring constantly. Reduce heat to low. Simmer, stirring often, until almost completely reduced, about 5 minutes. Stir in thyme and remaining ¼ teaspoon pepper. Remove from heat; set aside.

Step 6

Without separating individual rolls, cut roll loaf in half horizontally, creating 1 top and 1 bottom. Place roll bottom in prepared baking dish. Cover with cooked beef patty; spread patty with bacon jam. Add cheese and tomato slices; cover with roll top. Bake at 350˚F until cheese is melted and rolls are golden, about 8 minutes. Slice into sliders before serving with pickles.