Position a rack in the center of the oven and heat the oven to 400°F.
Line a large rimmed baking sheet with aluminum foil and set a rack over the foil. Arrange the bacon in a single layer on the rack, leaving no space between the slices.
Combine the brown sugar and red pepper flakes. Evenly sprinkle the mixture over the bacon, covering each slice completely.
Bake, rotating the sheet halfway through, until the sugar is melted and the bacon is brown and shiny, 20 to 30 minutes. Let cool on the rack for about 5 minutes, then loosen the slices from the rack with a metal spatula. Continue to cool for another 5 minutes before serving; the bacon will crisp as it cools.