Preheat oven to 350º F/ 180º C. Grease a 11 x 7 inch / 28 x 17 cm pan (or similar size) and line it with a sheet of parchment paper.

In a bowl combine coconut flour, almond flour and baking powder. Whisk and set aside.

Melt together the coconut oil and cocoa butter on a double boiler.

Pour the mixture into a mixing bowl and add the xylitol. Whisk for few minutes, until combined. If the xylitol is a fine powder, make sure no lumps remain (you can use a fork to break them).

Add the eggs, one by one, whisking well after each one. Add also the lemon zest or/ and extract.

Gradually add the dry ingredients, mixing gently with a spatula.

At the end mix in the chocolate chips.

Transfer the batter to the prepared pan. Smooth it out on top with the spatula.

Bake for about 30 minutes or until a toothpick inserted in the centre comes out clean.

Let the blondies cool until room temperature and then cover the pan with plastic wrap. Refrigerate for at least 2 hours or overnight before cutting into rectangular pieces.