Preheat your oven to 350°F (175°C).
In a mixing bowl, cream together the butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Mix in the vanilla extract.
In another bowl, whisk together the flour and baking powder.
Add the dry ingredients to the wet ingredients alternately with the milk, beginning and ending with the dry ingredients.
Pour the batter into a greased baking pan.
For the crumb topping, mix together the brown sugar, flour, melted butter, and cinnamon until crumbly.
Sprinkle the crumb topping evenly over the batter.
Bake for 40 minutes or until a toothpick inserted into the center comes out clean.
Let the cake cool before serving.