Cupcakes
1 1/4 cups all-purpose flour
1 1/2 teaspoons baking powder
1/2 teaspoon salt
1 teaspoon ground cinnamon (optional)

1/3 cup butter, at room temperature
1 cup white sugar
1 large egg
1 teaspoon vanilla extract
3/4 cup milk

Frosting
1/4 cup butter, room temperature
1/3 cup packed brown sugar
2 tablespoons milk
1 cup flaked coconut
2/3 cup chopped walnuts
1 teaspoon ground cinnamon

Preheat oven to 350 degrees F (175 degrees C). Line a 12 cup muffin tin with paper bake cups. Sift together the flour, baking powder, salt, and 1 teaspoon cinnamon.
In a large bowl, cream together 1/3 cup butter and white sugar until light and fluffy. Add the egg and vanilla and mix well. Pour in the flour mixture alternately with 3/4 cup milk; beat well. Fill the prepared muffin cups evenly, about half full.
Bake in the preheated oven until golden and the tops spring back when lightly pressed, 20 to 25 minutes. Remove from the oven and set aside to cool slightly.
Meanwhile, cream 1/4 cup butter with brown sugar until light and fluffy. Blend in 2 tablespoons milk until well combined and fold in the coconut, walnuts, and 1 teaspoon cinnamon.
With the warm cupcakes in the muffin pan, carefully spread about 2 teaspoons of the frosting on the center of each one. Do not spread the frosting all the way to the edge.
Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.
Broil the tops of the cupcakes in the preheated oven until coconut is lightly browned, 2 to 3 minutes.