Cream together the ½ cup butter and white sugar in a large bowl
Mix in the eggs
In a separate bowl, stir together the flour, baking powder and salt
Stir in the milk, a little at a time, alternating with flour mixture into the egg mixture. (A little milk, a little flour, etc...)
Fold in the blueberries
Spread in a greased 9x13 pan. Set aside
For The Topping
Mix together brown sugar, flour, Softened butter and cinnamon
Sprinkle over top of the blueberry coffee cake and bake in a greased 9x13 pan at 375° for 50 minutes or until cake tests done with a toothpick. *Remember, ovens may vary slightly so always allow a few minutes of wiggle room when following a recipe.*