Prep time 10 minutes
Cook time 55 minutes
Preheat oven to 350ºF. Line a square baking pan with parchment paper.
In a stand mixer add the flour, sugar and baking power. Mix on low. Add the softened butter and continue mixing on low.
Add the egg and oat milk and mix well on medium speed.
In a small bowl mix the brown sugar with the cinnamon.
Spread 1/2 the batter into the lined baking pan. Sprinkle 1/2 the cinnamon mixture over the batter. Spread the remaining batter evenly into pan. Top the batter with the apple slices, pressing them into batter. Sprinkle the other 1/2 of the cinnamon mixture over the apples and bake in oven for 50-55 minutes. Remove and cool.