1½ cups distilled white vinegar
½ cup cider vinegar
½ teaspoon kosher salt
½ teaspoon freshly ground black pepper
1 to 2 tablespoons red pepper flakes, depending on desired heat level
Warm the vinegars either in the microwave for 30 seconds or on the stovetop. You are warming them only, not boiling. Add the remaining ingredients, stir to dissolve the salt, and pour the mixture into a jar. Set aside for at least 1 day to let the flavors fully meld, then serve.
Store any remaining sauce in an airtight container at room temperature for up to 2 weeks. Shake well before using.