Prep : Preheat the oven to 375 degrees F. Spray a 9x13 baking dish with nonstick cooking spray.
Make The Crumble Topping : In a medium bowl, mix together the granulated sugar, light brown sugar, chopped pecans, and ground cinnamon until combined. Pour the melted butter over the dry mixture and blend with a fork.Stir in the bisquick baking mix until the mixture resembles coarse crumbs. Break up larger crumbles into smaller bits. 3/4 cup granulated sugar, 3/4 cup packed light brown sugar, 1/2 cup chopped pecans, 1½ teaspoons ground cinnamon, 12 tablespoons butter, 3 cups Bisquick baking mix
Make The Coffee Cake : In a larger bowl using an electric mixer, or use the bowl of a stand mixer with the paddle attachment, beat together the bisquick baking mix, milk, sour cream, granulated sugar, vanilla extract, and large eggs until well combined.* Do not overmix, but rather mix until it's thoroughly combined and no flour streaks remain in the batter, and then stop there. 3 cups Bisquick baking mix, 1 cup whole milk, 1/2 cup sour cream, 1/4 cup granulated sugar, 1 tablespoon vanilla extract, 2 large eggs
Spread half of the coffee cake batter evenly into the prepared baking dish. Sprinkle half of the crumb mixture evenly over the batter. Repeat with the remaining coffee cake batter and then end with the remaining crumb mixture on top.
Bake for 25-35 minutes, or until a toothpick inserted into the center of the cake comes out clean and the edges are lightly golden brown.
While the coffee cake is cooling slightly make the vanilla glaze. Add all the glaze ingredients into a small bowl and stir with a fork until combined. If it's too thick then add additional milk as needed and if it's too runny then add more powdered sugar as needed. Use a fork to drizzle the glaze over top the warm coffee cake.
1/2 cup powdered sugar, 3 tablespoons heavy cream, ½ teaspoon vanilla extract
This coffee cake is best served warmed (let it cool slightly before serving) or it can be served at room temperature as well.