Preheat oven to 350℉ (180℃)
Prepare a 8" round cake pan by lining the bottom with parchment paper or greasing the pan.
Core, peel, and chop two baking apples into ⅓-inch cubes. Set them aside to use in the cake batter. Reserve the red apple so you can slice it and place the slices on top of the cake before baking.
2 Medium Apples
Whisk flour, baking powder, salt and cinnamon in a small bowl. Set bowl aside for later.
1 ½ Cups Gluten-free flour, 1 ½ teaspoons Baking Powder, 1 teaspoon Salt, 1½ teaspoons Ground cinnamon
Place butter and granulated sugar in bowl of a stand mixer. Using the paddle attachment, begin mixing butter and sugar until light and fluffy (2 - 4 minutes), scraping bowl occasionally. Note: a hand mixer may also be used.
⅔ Cup Granulated Sugar, ¾ Cup Butter
Add room temperature eggs, one at a time, scraping bowl between each addition. Mix on medium-low speed until eggs are well incorporated.
3 Large Eggs
Add vanilla extract and mix for approximately 30 seconds,
1 teaspoon Vanilla extract
Add gluten-free flour mixture and mix on low speed until just combined. Scrape bottom and sides of bowl as needed.
Stir chopped apples into cake batter by hand. Stir in any additional optional ingredients such as walnuts, pecans, raisins, etc...
Pour cake batter into prepared pan and smooth the top lightly with spatula.
Core a red apple and slice it thinly, keeping the skin on. Arrange the slices in a spiral pattern on top of the cake batter.
1 Medium Red Apple, sliced thinly - do not peel
Sprinkle 1 tablespoon of granulated sugar evenly over top of cake.
1 Tablespoon Granulated Sugar
Bake for 40 - 50 minutes The cake top will be a golden color and a toothpick inserted in the center of the cake will come out clean when the cake is done.
Place cake on a rack and allow to cool completely before unmolding (approximately 40 minutes).
If desired, sprinkle confectioners' sugar over top of cake after unmolding.
2 Tablespoons Powdered sugar