Remove 2 eggs from fridge and set them on counter to come to start to come to room temperature.
Preheat your oven to 350 degrees F. Line and 8x8 glass baking dish with parchment paper (for easy removal). Set aside. Tip: Parchment paper can be tricky to get to stay in place. Crumble it up into a ball, and run it under your facet to make it damp. Then flatten it out and it will me much easier to work with.
Melt 1 cup of butter (melting butter the microwave can cause hot spots in your butter, so be sure to give it a good stir once melted. I prefer to melt it in a small sauce pan on the stove over medium heat, but either method will work).
While butter is melting, peal and mash 2-3 overripe bananas.
Using a mixer, cream together the melted butter with 1 cup of brown sugar and 1/2 cup of granulated sugar on low speed until light and fluffy (1-2 mins)
Add the 2 eggs, 1 tsp vanilla extract and the mashed bananas. Mix on a low speed until all wet ingredients are well combined.
In a separate mixing bowl, combine 2 cups of flour, 1 tsp baking powder and 1/2 tsp of cinnamon. Note: I use salted butter because that's what I keep in my house. If using unsalted butter, toss 1/2 teaspoon salt into the dry ingredients bowl as well. Gradually add the flour mixture into the batter. (I add about 1/2 cup at a time to ensure it gets well mixed into batter, mixing in between). Scrape down the sides of the bowl so all dry ingredients are completely mixed into batter.
Pour batter into the prepared pan with the parchment paper. Use spatula to evenly spread batter and smooth the top of the cake.
Bake for 40-45 minutes, or until the center of cake is no longer wobbly, and a toothpick inserted in the center of the cake comes out clean. Note: baking time can vary in different ovens, so keep a close eye on it and make sure its fully baked through in center before pulling it out so the center of your cake doesn't sink as it cools.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack. Remove parchment and let cake cool completely.
Once cooled, transfer to a serving platter or cake stand, and spread a generous layer of store-bought vanilla frosting over the top of the cake. I like to leave the sides unfrosted.
Lightly sprinkle coarse or flakey salt over the top of the frosting. This will help enhance the sweetness and create the most intriguing salty/sweet combination with each bite. Slice into 9 square slices. If you'd like to add a garnish, add thin banana slices or a Nila Wafer cookie to the top of each piece of cake.