1 tablespoon butter 1 strip bacon, cut crosswise into thin slivers 1 small onion, peeled and finely chopped ⅔ cup cider vinegar ⅔ cup brown sugar (dark or light), or to taste ⅔ cup Dijon mustard 1 tablespoon of your favorite hot sauce, or to taste Coarse salt (sea or kosher) and freshly ground black pepper, to taste
In a saucepan, melt the butter over medium heat. Add the bacon and onion and cook, stirring with a wooden spoon, until the onion is golden brown, 6 to 8 minutes. Stir in the cider vinegar and bring to a boil. Whisk in the brown sugar, mustard and hot sauce. Reduce the heat and gently simmer the sauce until mellow and richly flavored, 10 minutes. Correct the seasoning, adding salt, pepper and additional sugar or hot sauce as needed — the sauce should be sweet, tart, piquant and very flavorful. Cool to room temperature for serving. This makes about 2 cups sauce.