Pre-roast your apple slices until tender. You can do this in a pan with a splash of water and a sprinkle of cinnamon until they soften, or bake them briefly beforehand.

In a large mixing bowl, whisk together the almond flour, coconut flour, baking powder, and erythritol. Ensure there are no large clumps of almond flour.

In a separate bowl, beat the eggs. Add the Greek yogurt, milk, melted butter (ensure it is not hot so it doesn't cook the eggs), vanilla extract, and the citrus zests. Mix until smooth.

Gently pour the wet mixture into the dry ingredients. Stir until fully incorporated. The batter will be denser than traditional wheat batter due to the absorbent nature of coconut flour.

Preheat your oven to 400°F. Grease a rectangular loaf pan or line it with parchment paper. Pour the batter into the pan and arrange the roasted apple slices on top in a decorative pattern.

Lower the oven temperature to 350°F and bake for approximately 40 minutes.

The Toothpick Test: Insert a toothpick into the center; if it comes out clean, it’s done.

Pro Tip: If the top is golden brown but the center is still wet, cover the pan with aluminum foil for the final 10 minutes to prevent burning.

Remove from the oven and let it cool completely in the pan before slicing. Because this cake uses nut flours, it needs time to "set" its structure as it cools.