Peel and core apples; slice 1/4-inch thick. Set aside.
Use butter or nonstick spray to grease an 8-inch cake pan or 10 inch cast iron skillet. If you plan to remove the cake from the pan for serving, line bottom of the pan with parchment paper. Heat oven to 350°F.
Whisk flour with baking powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer, or large bowl with a hand mixer, beat granulated sugar with 1 cup (2 sticks) of butter for 3-4 minutes, until lightened in color and fluffy in texture.
Beat in eggs, one at a time, then almond extract, and beat mixture about 2 minutes, or until creamy. If the mixture appears curdled, spoon in one or two tablespoons of your dry ingredients and continue mixing.
Gradually add flour mixture in three batches, alternating with buttermilk, mixing after each addition. Do not overmix. Some flour streaks should still be visible at this point. Fold most of the apple slices into the batter, leaving about 1/4 of them to place on the top.
Place batter in prepared pan and press and smooth with an offset spatula, making sure there is batter in all the corners of the pan.
Arrange remaining apple slices on top of batter in concentric circles, gently pressing them in a bit, and smoothing the batter. Scatter almonds on top. Sprinkle with sparkling or raw sugar, if desired.
Place in the oven and bake at 350°F for 45 minutes to an hour, or until a cake tester comes out clean, the top has browned, and the apples no longer feel firm when pierced with the tester.
Allow to cool in the pan until just warm, then transfer to a rack and sprinkle with powdered sugar. Serve in the pan, or remove from pan and transfer to a plate.
Slice with a serrated knife and serve.