Easy Bisquick Mix Apple Coffee Cake

This is an easy coofee cake to put together,
the trouble I have is in making the topping
I never seem to make enough,double the quantities.

Ingredients:
Cake:
2 cups Bisquick mix
2/3 cup of milk or water
2 Tbsp sugar
1 egg
1 tart green apple, cored, peeled, sliced

Topping:
1/3 cup Bisquick mix
1/3 cup packed brown sugar
1/2 tsp ground cinnamon
4 Tbsp butter

Directions:
Preheat oven to 400 degrees F.
Grease 8" square pan or 9" round pan.
Mix cake ingredients.
Spread cake batter in pan.
Insert apple slices into the batter
evenly throughout the cake.
Mix the topping ingredients of Bisquick,
brown sugar and cinnamon.
Spread topping mix over top of batter in pan.
Add slices of butter all over the top.
Bake 20 minutes or until golden brown,
testing with a toothpick.