Line the bottom of a 9-inch cake pan with parchment or wax paper, optional. Spray pan with non-stick cooking spray.
Mix brown sugar, 2 tablespoons sugar, walnuts and cinnamon together in a small bowl. Reserve 3/4 cup for filling. Add 1/4 cup Bisquick and 2 tablespoons butter. Stir until mixture forms coarse crumbs. Set Aside.
Combine butter and sugar in a large bowl until well-blended. Stir in eggs and sour cream until well-blended. Stir in Bisquick until just mixed. Spread 1/2 of batter into prepared pan. Sprinkle with reserved filling. Top with dollops of remaining cake batter; smooth using a spatula. Sprinkle with crumbled streusel.
Bake for 50 to 60 minutes or until a toothpick inserted into the center comes out clean. Let cool 15 minutes in pan. Run a knife around the outside edge of the cake and invert onto a plate. Invert again onto a cooling rack, optional. Eat warm or at room temperature.
Find it online: https://livelaughrowe.com/sour-cream-crumb-cake-recipe/