Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan.
In a large bowl, cream together the softened butter and brown sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition, then stir in the mashed bananas.
In another bowl, whisk together the flour, protein powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
While the cake cools, prepare the salted caramel sauce.
In a saucepan, melt the granulated sugar over medium heat until it turns amber.
Once the sugar has melted, carefully add the heavy cream, stirring until smooth.
Remove from heat and stir in the sea salt to taste.
Once cooled, slice the cake and drizzle generously with the salted caramel sauce.
