Cinnamon Swirl Coffee Cake

for the cake:
2 tbsp butter, softened
1/2 cup sugar
1/2 tsp salt
1 egg
2/3 cup milk
1 tsp vanilla extract
1-1/2 cups flour
3 tsp baking powder

for the cinnamon swirl:
1/4 cup sugar
2 tbsp flour
1 tsp cinnamon
1/4 cup cold butter, cut into small pieces

for the glaze:
1 cup powdered sugar
1/2 tsp vanilla
2-3 tbsp milk

Preheat oven to 350.
Beat the butter, sugar and salt in the bowl of a stand mixer.
Add in the egg, milk, and vanilla, mixing smooth.
Gradually beat in the flour and baking powder, beating until smooth.
Pour into a greased 8-inch baking pan. Combine the sugar, flour, cinnamon, and butter. Stir together until smooth.
Break the cinnamon mixture into small pieces, and evenly distribute across the top of the cake mixture, in a swirl pattern. 
Bake for 25-30 minutes, or until a toothpick inserted in the middle comes out clean. 
Stir together the powdered sugar, vanilla, and milk until it reaches a thin consistency; pour over the warm cake.
Serve warm.