Pre-heat oven to 350 F.; line a 9-by-9-inch pan with parchment paper (or grease and flour).

Melt 4 tablespoons butter in a saucepan; remove from heat and add 1/4 cup granulated sugar, the brown sugar, 3/4 cup gluten-free flour blend, the cocoa powder and a pinch of salt. Stir with a fork, breaking up any large clumps, and spread out onto a baking sheet. Set aside.

Combine 1/4 cup granulated sugar and the cinnamon in a small bowl; set aside.

Beat the remaining 8 tablespoons butter with the remaining 1 cup sugar until light and fluffy. Add the eggs, vanilla and sour cream and beat again. Add the remaining 2 cups gluten-free flour blend, baking powder, baking soda, instant espresso, and a pinch of salt and beat again.

Spread half the batter into your prepared pan – use a small angled spatula to spread evenly. Top with the cinnamon-sugar and sprinkle with half the chocolate chips. Top with the remaining batter; use a small angled spatula to spread evenly. Top with the streusel and sprinkle with the remaining chocolate chips.

Bake cake for 45 minutes or until a cake tester tests clean. Cool completely in the pan on a wire rack.