Step 1: Prepare Your Baking Environment
Begin by preheating your oven to 350 degrees Fahrenheit (175 degrees Celsius). Take two 4-inch or 6-inch mini springform cake pans and grease them lightly with coconut oil or line them with unbleached parchment paper. Ensuring your pans are properly prepped prevents sticking and guarantees your layers will pop out flawlessly.Step 2: Mash and Combine the Wet Ingredients
In a large mixing bowl, peel your overripe bananas and mash them vigorously with a fork until they form a smooth, nearly liquid puree. A few small lumps are perfectly fine and add wonderful texture. Whisk in the unsweetened applesauce, the two large eggs, and the pure vanilla extract. Beat the mixture until it is fully integrated and slightly frothy, which helps aerate the batter for a softer crumb.Step 3: Whisk the Dry Elements
In a separate, medium-sized bowl, measure out your oat flour, Ceylon cinnamon, and baking powder. Whisk these dry elements together thoroughly. This critical step ensures that the baking powder is evenly distributed, which prevents lopsided baking and ensures a uniform rise across both of your cake layers.Step 4: Fold the Batter Together
Gently pour the dry oat flour mixture into your bowl of wet ingredients. Using a silicone spatula, fold the ingredients together using a sweeping, bottom-to-top motion. Be careful to stop mixing as soon as you no longer see any dry pockets of flour. Overmixing oat flour can activate too much starch, resulting in a rubbery texture rather than the light, fluffy consistency a baby needs.Step 5: Bake to Perfection
Divide the batter evenly between your two prepared baking pans, smoothing the tops lightly with the back of a spoon. Place them in the center rack of your preheated oven and bake for 22 to 25 minutes. You will know they are done when a toothpick inserted into the center comes out completely clean, and the edges begin to pull away slightly from the sides of the pan.Step 6: Cool and Frost
Allow the layers to cool in their pans for 10 minutes before transferring them to a wire cooling rack. They must reach room temperature before frosting; otherwise, your topping will melt into a puddle. Once cooled, generously slather the thick, chilled full-fat Greek yogurt between the two layers and all over the exterior. You can use an offset spatula to create rustic, bakery-style swirls.