To make a plain gluten-free coffee cake, just omit the peaches and blueberries. If you like, you can add a cinnamon sugar swirl to the cake though. Place half of the cake batter on the bottom of the pan. Combine 100 grams of brown sugar with 2 teaspoons of ground cinnamon and sprinkle evenly over the cake batter. Top with the remaining cake batter and streusel. Bake as directed.