Step 1

Cut 6 slices thick-cut bacon crosswise into 1/2-inch pieces. Place in a large skillet in a single layer and cook over medium heat, stirring occasionally, until the fat is rendered and the bacon is browned and crisp, 10 to 12 minutes. Meanwhile, finely dice 1 small shallot (about 2 tablespoons).

Step 2

Use a slotted spoon to transfer the bacon to a paper towel-lined plate. (Reserve the bacon for another use.) Pour the bacon fat through a fine-mesh strainer into a heatproof liquid measuring cup or bowl. Wipe the skillet clean and remove any bacon solids with a paper towel.

Step 3

Return 1/4 cup of the bacon fat to the skillet and heat over medium heat until shimmering. Add the shallot and cook, stirring occasionally until just softened, about 1 minute. Add 3 tablespoons apple cider vinegar, 1 tablespoon packed light brown sugar, 1 teaspoon Dijon mustard, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Cook, whisking constantly, until emulsified and the sugar is dissolved, 20 to 30 seconds. Use immediately.