Preheat your oven to 160°C (320°F) with the fan setting on (see note 1 if your oven doesn’t have a fan function). Prepare two 8-inch cake tins by greasing and/or lining them—homemade cake release works well for this. In a bowl, sift together the flour, cornstarch, baking soda, baking powder, salt, and ground cinnamon. Use a whisk or fork to mix everything evenly and set aside. Mash the bananas thoroughly with a potato masher or fork and set them aside for now.
In a large mixing bowl, combine the butter, vegetable oil, and sugar. Using an electric mixer—hand or stand mixer both work fine (see note 2)—cream the ingredients together for about 2 minutes until the mixture is light and creamy. Add the eggs one at a time, mixing well for about 10-15 seconds after each addition. Next, add the mashed bananas, vanilla extract, and Greek yogurt, mixing on medium speed until fully incorporated. The batter may appear slightly curdled at this point, but that’s normal.
Set your mixer aside and finish mixing the batter by hand. Gradually fold in the pre-mixed dry ingredients using a spatula until just combined, ensuring there are no visible streaks of flour. Be careful not to overmix (see note 3). Pour the batter evenly into the two prepared 8-inch tins, then gently tap the tins on the counter to release any large air bubbles. Bake for about 40 minutes or until a toothpick inserted in the center comes out clean.
Once baked, let the cakes cool in their tins for 15-20 minutes before transferring them to a wire rack to cool completely. Wait until fully cooled before filling or topping with caramel and cream cheese frosting.