Preheat your oven to 350°F (175°C). Grease a 9x9 or 9x11-inch baking dish.

In a large mixing bowl, combine the granulated sugar, brown sugar, and softened butter. Beat until light and fluffy, about 3-5 minutes.

Add the eggs, vanilla extract, buttermilk, maple syrup, and mashed bananas to the creamed mixture. Blend until smooth, about 2-3 minutes.

In a separate bowl, whisk together the gluten-free flour, baking powder, baking soda, kosher salt, and ground cinnamon.

Gradually add the dry mixture into the wet batter, folding gently until just combined.

Pour the batter into your prepared baking dish and tap gently on the counter to eliminate air bubbles.

Bake for 45-55 minutes, checking for doneness with a toothpick.

While the cake bakes, melt the butter and brown sugar in a saucepan over medium-low heat until smooth, about 3-5 minutes.

Stir in the heavy cream and vanilla, cooking until the sauce thickens slightly, about 2-3 minutes.

Once the cake is out of the oven, allow it to cool for 10-15 minutes. Poke holes across the top and pour the warm toffee sauce over it.

Let the cake soak in the sauce for at least an hour before serving.

Slice the cake into pieces and serve warm with additional toffee sauce if desired.