Whisk the yellow mustard, apple cider vinegar, light brown sugar, honey, kosher salt, ground black pepper, and cayenne pepper together in a small saucepan until smooth.
Set over low heat and bring to a gentle simmer, stirring occasionally, 3–5 minutes, until the sugar dissolves and the sauce looks glossy and slightly thickened.
Remove from heat and let cool to room temperature, about 20 minutes. Transfer to a jar, then refrigerate or use immediately with pork or chicken.