- Preheat an oven to 350°F. Grease a 9-inch round springform pan. Line the bottom with a round of parchment paper and grease the paper.
- To make the topping, in a small bowl, stir together the flour, sugar, cinnamon and ginger. Add the butter and, using a pastry cutter or your fingers, cut or rub in the butter until coarse crumbs form. Set aside.
- To make the cake, coarsely chop the macadamia nuts and set aside.
- In a bowl, stir together the all-purpose and cake flours, granulated and brown sugars, baking powder, baking soda and salt.
- In another bowl, whisk together the sour cream, eggs, oil and vanilla until well blended. Stir the sour cream mixture into the flour mixture. Using an electric mixer on medium speed or a wire whisk, beat until smooth and creamy, about 1 minute.
- Spoon half of the batter into the prepared pan and spread evenly. Sprinkle evenly with half of the topping. Cover evenly with the remaining batter. Sprinkle evenly with the nuts, gently pressing them into the batter, then cover with the remaining topping.
- Bake until the topping is golden brown and a toothpick inserted into the center of the cake comes out clean, 40 to 45 minutes. Transfer the pan to a wire rack and let cool for 20 minutes. Remove the sides of the springform pan, if using. Serve the cake warm or at room temperature, cut into wedges. Makes one 9-inch cake.
- Note: If macadamia nut oil is not available, canola oil may be substituted.