Preheat oven to 425º F. Brush melted butter on the inside of your fry pan.
In a stand mixer, cream the butter and sugar until pale and fluffy. On medium-low speed, add eggs and turn off the mixer to scrape down the sides of the bowl. Add the smashed bananas and continue mixing. Scrape down the sides of the bowl. Add the dry ingredients (all-purpose flour, baking soda, kosher salt) and continue mixing until the batter is well combined. Pour the batter into the pan to fill half-way.
Place on a sheet pan and bake in the oven for 10 minutes. Remove and top with sliced bananas if you like. Continue baking for 30 minutes. Brush with melted butter to finish.