Pour the melted butter into an ungreased 9×2 inch pie dish or round cake pan. (Make sure the pan is 2 inches deep. I recommend this pie dish, which is 1.8 inches deep but I never have an overflow issue.) Sprinkle brown sugar evenly over butter.

Pat the pineapple and cherries with paper towels until they’re very dry. (Wet fruit will make a soggy cake.) Arrange 6-7 pineapple slices and all the cherries on top of the brown sugar. Halve 3 pineapple rings and arrange them around the sides of the pan. (See my photo.) Place the pan in the fridge while you prepare the cake batter to help set the arrangement.

Preheat the oven to 375F. In a medium bowl, whisk together the gluten-free flour, baking powder and salt.

In the bowl of a stand mixer, add the egg whites and sugar. Whip on medium-high speed for 3 minutes, until light and fluffy. With the mixer running on low, slowly drizzle in the oil. (You want to do this slowly so you don't lose the air that you've mixed in.) Mix in the vanilla and lemon juice.

With the mixer on low, add ⅓ of the dry ingredients. Mix until incorporated. Add the sour cream and mix to combine. Add another ⅓ of the dry ingredients and continue to mix. Add ½ of the milk followed by the last ⅓ of the dry ingredients. Add the remaining milk and stir until totally combined. (You want to add the dry ingredients alternately with liquid ingredients so the flour absorbs into the batter.)

Pour the cake batter into the prepared pan. Bake for 40-45 minutes until the center of the cake is cooked through. You can cover the top of the cake with foil towards the end of the bake time if it starts to brown too quickly.

Remove cake from the oven and cool on a wire rack for ONLY 20 minutes. Invert the slightly cooled cake onto a cake stand or serving plate. Cool the cake completely to room temperature before slicing and serving. (Do not refrigerate the cake to speed up the cooling or it will be dense.) Slice, top with whipped cream and enjoy!