Maple frosting: In a small saucepan over medium heat, bring 1/2 cup maple syrup, 2 Tbsp. butter, and 1 Tbsp. milk to a simmer - let simmer for 2 minutes while you are stirring. Remove from heat, whisk in 1 tsp. vanilla and then gradually add in 1-1.5 cups powdered sugar. Spread on top of muffins once cooled.