Start by preheating the oven to 350 degrees Fahrenheit and lightly butter (or line with parchment paper) your brownie pan or square pan.
Whip together the unsalted butter, peanut butter, brown sugar, and pure cane sugar, in the bowl of an electric mixer on medium-high speed until smooth and creamy.
Turn speed to low and add egg, mashed banana, vanilla extract, coconut milk, and mix until well combined.
In the meantime, whisk together all-purpose flour, sea salt, and baking soda in a separate bowl and add dry ingredients to mixture and continue to mix until fully incorporated.
Now, add 1 tablespoon of batter into each brownie cavity, pressing down with your fingers (or add ⅔ of batter to bottom of square pan, spreading and flattening with hands), before sprinkling chocolate chips on top.
Pour sweetened condensed milk (1 tablespoon for each brownie cavity) over first layer with chocolate chips, and then spoon remaining batter (1 tablespoon at a time) over the condensed milk. **Be sure to spread around dough to ensure that top is completely covered.**
Once done, bake for 30-35 minutes, until tops of cookie bars are brown and the middle is set.
Remove from oven and let it cool fully before removing them from brownie cavities (or slicing them into squares from the baking pan).
They are absolutely gooey so be careful not to make your hands too sticky. Sprinkle lightly with powdered sugar if desired.
Bon Appetite!