Grease a 9 x 13 baking pan and preheat oven to 400.
In a mixing bowl, cream the butter and sugar together.
Add in milk and eggs, and mix well.
Add in 3 cups flour, baking powder, and salt.
Pour batter into greased pan. Set aside.
In a separate bowl, combine the 1/2 cup flour, sugar, cinnamon, and butter.
Using a pastry blender or two butter knives, cut in butter until crumbs are formed.
Sprinkle topping over cake batter.
Place pan in oven and bake for 25-30 minutes, or until toothpick comes out clean once inserted in center.
Remove from oven and enjoy!