Begin by melting ½ cup of butter over low heat in a saucepan. Stir constantly until it becomes a nutty brown color, about 5-7 minutes.

Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking pan by greasing it or lining with parchment paper.

In a medium bowl, whisk together 1 ½ cups of gluten-free flour, 1 tsp of baking soda, ¼ tsp of kosher salt, and ½ tsp of ground cinnamon.

In a large mixing bowl, combine the cooled brown butter, ½ cup of brown sugar, ½ cup of granulated sugar, and 1 tsp of vanilla extract. Beat until creamy.

Gradually add in 2 large eggs, mixing well after each addition, then fold in 3 mashed ripe bananas until smooth.

Slowly add the dry ingredients to the wet mixture, gently folding them together until just combined.

Pour the batter into the prepared baking pan and smooth the top. Bake for 40-45 minutes, or until a toothpick comes out clean.

Cool the cake in the pan for about 10-15 minutes, then carefully lift it out and allow to cool completely.

For the salted caramel, combine 1 cup of granulated sugar and ¼ cup of water in a saucepan over medium heat. Stir gently until dissolved, then simmer until golden, about 8-10 minutes.

Whisk in ½ cup of heavy cream and ¼ cup of butter until smooth before cooling completely.

Whisk together 2 egg whites and ½ cup of granulated sugar over simmering water until dissolved. Beat until stiff peaks form, then gradually mix in ½ cup of softened butter and caramel sauce.

Spread the salted caramel buttercream over the cooled cake, optionally drizzle with more caramel sauce and sprinkle with flaky sea salt.