Grease the pan. For easy removal of the cake, place parchment paper on the bottom of the cake pan. Then grease the sides. Preheat oven to 350°F. Mash the bananas and set aside as you prep the rest of your ingredients.
1 cup mashed bananas
In a large bowl, add oil, vanilla, mashed bananas, brown sugar, and eggs.
1/2 cup oil, 1 tbsp vanilla, 2 eggs, 3/4 cups dark brown sugar, 1 cup mashed bananas
Add in the flour, baking powder, baking soda, cinnamon, and salt. Using a rubber spatula, gently fold it in until a soft batter forms. It will be runny.
2 cups flour, 1 3/4 tsps baking powder, 1/2 tsp baking soda, 1/2 tsp cinnamon, 1/2 tsp salt
In a small bowl, combine the melted butter and brown sugar. Place evenly along the bottom of the prepared pan. Then sprinkle blueberries on top. Make sure it is all evenly distributed.
2 tbsp butter, 1/4 cup dark brown sugar
Take the cake batter and gently spread it on top of the blueberries, making sure not to disturb the layer of them. I like to use a cookie scooper for this as I find it's effective and not messy. Spread evenly.
2 cups blueberries
Bake for 45-50 or until the cake come out clean with a toothpick inserted in the middle.
Allow to cool, then gently run a knife around the cake pan. Flip the cake upside down onto a flat surface like a plate or a cake stand. Peel the parchment paper off to reveal the gorgeous blueberry layer! Then slice, and enjoy!