Preheat your oven to 180°C (350°F) and line a loaf pan with parchment paper, lightly greasing the sides to prevent sticking.

In a large mixing bowl, add almond flour, coconut flour, baking powder, and salt, then whisk thoroughly until evenly combined and no lumps remain.

In a separate bowl, crack the eggs and whisk them together with melted butter, almond milk, sweetener, and vanilla extract until the mixture becomes smooth and slightly creamy.

Gradually add the dry ingredients into the wet mixture, stirring gently until a thick, smooth batter forms without any dry pockets.

Divide the batter evenly into two bowls, keeping one portion plain for vanilla and mixing cocoa powder into the second portion until fully blended.

Pour alternating layers of vanilla and chocolate batter into the prepared pan, creating a natural layered effect.

Take a toothpick or knife and gently swirl through the batter in circular or zigzag motions to create a marble pattern, being careful not to overmix.

Place the pan in the oven and bake for 35–45 minutes, checking doneness by inserting a toothpick into the center—it should come out clean.

Remove from the oven and allow the cake to cool in the pan for at least 15 minutes before transferring it to a wire rack to cool completely.

Slice carefully once cooled and serve as is or with your favorite keto toppings.