Preheat the oven to 325°F. Line two cupcake pans with liners and set aside.
In a large mixing bowl, beat the egg whites, salt, and cream of tartar on medium speed until foamy, about 4 minutes. Slowly beat in the sugar and keep beating until the mixture holds soft peaks.
In a small bowl whisk together the gluten free flour and tapioca. Sift this mixture over the egg whites and gently fold in.
Spoon the batter into the prepared cupcake tins to about ¾ full. Bake until the cupcakes are set, the edges are very lightly browned, and the top springs back when pressed lightly, about 20 minutes.
Allow the cupcakes to cool for 10 minutes in the pan, then remove and place on a wire rack to cool completely.
Make the Filling
In a large bowl, using an electric mixer, beat the cream with the powdered sugar until soft peaks form.
Assemble
Cut the cupcakes in half, and place a generous spoonful of the whipped cream on the bottom layer, then top it with sliced strawberries. Place the other half of the cupcake on top, and serve.
Notes
Tips
When making the shortcakes: Use room-temperature egg whites. This is an angel food cake recipe, which relies on egg whites to help it rise. Bringing the egg whites to room temperature is the first essential step. Room-temperature egg whites will froth up much quicker and will retain more air.
Use store-bought whipped cream: In my opinion, homemade is always best. However, in the interest of time, you can use store-bought whipped cream to fill these shortcakes.
Try other berries: Make this as blueberry, blackberry, or raspberry shortcakes by swapping the strawberries for other seasonal berries. Or, do a combination.
Add vanilla: A little pure vanilla extract adds a delicate vanilla flavor and fragrance to the shortcakes. You can add it in when you beat the eggs with the cream of tartar.
Add citrus: You can also add a little citrus zest to the shortcake batter. My preference is for orange zest because it so beautifully complements the strawberries, but lemon zest is also nice. Fold it into the batter when you add the flour.
Sift the powdered sugar: If making your whipped cream, make sure to sift the powdered sugar first to eliminate any lumps. Or, if you like things less sweet, you can leave it out.