Preheat oven to 350ºF. Line 18 muffin holes with paper liners.'
Place sugar and butter in a large bowl; cream with an electric mixer until light and fluffy. Add egg and vanilla; beat until thoroughly mixed.
In another large bowl, mix together flour, baking powder and baking soda. Add half of flour mixture to butter mixture; beat well with mixer. Add milk and remaining flour mixture; beat until batter is combined and then fold in mashed bananas.
Spoon batter into muffin liners about ¾ full. Bake until muffins start to brown and a tester inserted in center of a muffin comes out clean, about 25 to 30 minutes. Allow muffins to cool in pan for about 2 minutes; remove to a wire rack and cool completely before icing.
Meanwhile, combine icing ingredients in a medium bowl; beat with an electric mixer until creamy, about 1 to 2 minutes. Ice cooled muffins; cover and refrigerate any uneaten muffins. Yields 1 muffin per serving.
Recipe by In Good Taste at http://ingoodtaste.kitchen/banana-muffins-lemon/