Preheat oven to 350F. Line the bottom of a 9-inch springform pan with parchment paper, and grease the paper and sides of the pan with butter or oil for good measure.

Sprinkle crumbled cookies or sliced almonds along the bottom of the cake pan. This will help soak up the juice of the apples as they cook, and create a nice topping.

Peel and core your apples. Then, slice each apple into thin circles of about ¼ inch. You can also cut them into slices or even cubes, but keeping the apples in circles will result in a nice design on the top of the cake.

Arrange the apples directly on top of the crumbs or sliced almonds in the prepared pan, layering them in as many layers as necessary. Sprinkle with ¼ cup sugar. Dot the butter in a circle, keeping  to about 1 inch from the sides of the pan, and leaving the center of the cake bare.

In a standing mixer or in a large bowl using an electric mixer, beat the eggs with the sugar until thick and pale yellow and ribbons are formed along the sides, about 8-10 minutes. Gently fold in vanilla, then gradually add in the gluten-free flour and salt in two batches, folding just until combined after each addition.

Pour the batter over the apples. Use an offset spatula or spoon to try and flatten out the top, helping the batter get in between all the apple slices and all the way to the bottom. Let gluten-free apple cake stand for 5 minutes for the batter to settle fully.

Transfer to 350F oven for 1 hour, until the gluten-free apple sharlotka is golden on the top, and a cake tester inserted in the middle comes out clean. Transfer pan onto a cookie drying rack and let cool for 15 minutes. Flip out onto a large plate or cutting board, unmold the cake pan and remove parchment paper, then transfer onto a serving platter or cake stand so that the apple slices and crushed cookies or almonds are at the top.

Dust with confectioners' sugar and serve. Cake can keep in the fridge for 5 days.