Whip eggs: Add 6 eggs to a large mixing bowl and whip on high for a minute or two. Then, gradually add 1 cup of granulated sugar between the bowl and the whisk as it continues to whip.

Now, whip until pale in color, fluffy, and a ribbon of batter flowing off the whisk doesn't disappear into itself for 2-3 seconds (stand mixer - ~20 minutes; if you use a double wired whisk (11 wires, instead of 6) it will take only ~7 minutes; hand mixer will take more than ~20 min).

While the eggs are whipping prep the rest of the recipe:

Preheat oven to 350F° with the baking rack centered.

Line a 9" round pan with parchment paper or butter the inside of the pan, then dust with flour and shake out excess. If you have a baking strip, wet it and fasten around the pan. Set aside.

Prepare the apples: Peel, core, and slice the apples into 1/4" slices. Add 2 tbsp of flour and toss to coat. Set aside. Cutting the apples into slices rather than cubes means that they are less likely to sink to the bottom as the cake bakes.

Add dry ingredients: Once the eggs are properly whipped, sift 1 cup of flour in thirds right into the whipped eggs, carefully folding after each addition and trying not to deflate the batter as much as possible.

Layer inside the pan: now make 3 layers with the sponge cake & apples starting with the sponge cake batter and finishing with the apples.

Sprinkle the top: Lastly, sprinkle the 2-3 tbsp of sugar on top, then 1/2 almond slices, if using.

Bake: Place the filled baking pan on a bigger baking sheet (this will catch any accidental drips) and bake for ~60 minutes, or until a toothpick inserted into the middle comes out clean.

Then, remove from the oven and cool for 5 minutes. Now, run a thin knife along the inside edge of the pan and carefully invert the cake onto a cooling rack. Peel off the parchment paper. Leave to cool completely before slicing and serving.

The cake is best eaten the same day it is made. Store on the counter under a cake dome.