This sauce is butter based so it does not require a thickener. However, sauces that have additional liquid like broth can be thickened by adding some cornstarch or flour (Xanthan Gum is best for low-carb) and stir over medium-high heat until it thickens. To prevent the thickener from clumping, you can mix it with liquid or some of the melted butter before adding it to the saucepan.