Preheat oven to 350°F/ 180°C and line a cupcake tray with silicone cases or aluminum cases. Add the almond flour, coconut flour, baking powder, 3 tablespoons erythritol, and sea salt to a large bowl, and loosely mix through. Add the mozzarella and cream cheese in a heatproof bowl and place in the microwave for 1 minute on high until melted. Add 1 egg to the melted cheese and loosely give it a stir through. Make a well in the center of the dry ingredients then use your hands to knead until a ball of dough comes together. Flatten to a disc shape and place the dough between 2 sheets of baking paper. Use a rolling pin to roll out the dough to a disk approximately ¼-inch / 6mm thickness, then peel off the top layer of baking paper.

Use a 3 ¼”/ 8cm cookie cutter to cut out disks of pastry and carefully place them into the silicone case. Re-roll any scraps of dough to yield more pastry cases. Shape and neatly tuck the edges of the pastry and prick the base of each pie crust with a fork. Any leftover pie crust can be reserved for making a lattice top or rolled thinly and used to cut smaller circles to cover the pie tops.

Prebake the pie crusts in the center of the oven for 10-12 minutes or until just beginning to golden and crisp up. Once ready, the pastry will have puffed up slightly, so use a small flat base, like the base of a wine bottle cork or the back of a small spoon to press the crust base and sides to make the pastry tighter and sturdier for the filling. Set aside to fully cool.

Add the mixed berries to a small saucepan set over medium heat. Add the erythritol, lemon juice, ground chia seeds, vanilla extract, almond extract, and lemon extract (optional). Bring to a gentle simmer. Keep stirring until the chia seeds have worked their magic and thickened the mixture.

Preheat oven to 350°F/ 180°C. Transfer the berry mixture to a blender or food processor. Pulse to a smooth consistency. Pour the berry filling into each of the pie crusts. Set aside. Any leftover mixture can be frozen and used in other recipes or in a smoothie.

If making a top layer for the pies, roll out the remaining crust dough between the baking paper at approximately 1/16th-inch / 4mm thickness. Cut strips with a pizza roller to make a lattice design, or cut smaller circles to entirely cover the berry filling, or try star shapes for another pretty look.

Bake the pies in the center of the oven for a further 10 minutes until the tops are golden and crisp. Remove from the oven and set aside to cool to room temperature. Dust with powdered sweetener for presentation marks (optional).