Add butter to a large skillet and warm over medium-high heat until melted.
Add Brussels sprouts to the skillet, sprinkle with salt and pepper, and cook undisturbed for 3-4 minutes until the bottoms have browned.
Add vinegar, maple syrup and mustard and stir until incorporated.
Continue to cook Brussels sprouts for 1-2 minutes more, stirring frequently, until softened. Do not overcook or Brussels sprouts could become mushy.
Serve immediately.
Calories: 76kcal, Carbohydrates: 9g, Protein: 3g, Fat: 4g, Saturated Fat: 2g, Cholesterol: 10mg, Sodium: 256mg, Potassium: 302mg, Fiber: 3g, Sugar: 4g, Vitamin A: 687IU, Vitamin C: 64mg, Calcium: 35mg, Iron: 1mg