To prepare a sweet potato doughnuts maple icing recipe, you'll first need to prepare the sweet potatoes. Peel and cut the Sweet Potatoes in half lengthwise. Cut each half into 1/4-inch slices. Place the slices in the bowl of an electric mixer fitted with the paddle attachment. Beat the mixture on medium-high speed until it's light and fluffy, about 2 minutes. Add the sugar and vanilla and beat until combined. Gradually add the milk and mix until smooth. Pour the batter into the greased muffin tins and bake for 12 to 15 minutes or until golden brown. Remove the muffins from the oven and allow them to cool for 5 minutes before serving.