Preheat the oven to 350 F, grease or line a 9x9 baking pan with parchment and set aside
In a large mixing bowl, stir together the bisquick, granulated sugar, and cinnamon.
2 ½ cups bisquick, ¼ cup granulated sugar, ½ teaspoon cinnamon
Mix in the sour cream, milk, and egg until well blended. Transfer the mixture to to the prepared pan
1 cup sour cream, ½ cup milk, 1 large egg
Add the bisquick, brown sugar, and cinnamon to a separate large bowl and mix well. Cut in the butter until the mixture is crumbly. Sprinkle on top of the cake.
1 cup bisquick, 1 cup lightly packed brown sugar, 2 teaspoons cinnamon, ⅓ cup butter
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool before slicing and serving.