Preheat oven to 350.
Spray a 9x12 baking dish with non-stick spray and set aside.
Prepare the streusel – combine all the ingredients until crumbly- set aside.
To make the cake- Cream the butter and sugar together until light and fluffy (4 minutes)
Add the milk until combined. (it may look weird at this point!)
Add the egg and vanilla extract and mix until smooth.
Add the dry ingredients and combine.
Fold in the chocolate chips.
Pour into prepared pan.
Top with streusel topping
Bake for about 40 minutes or until done.