In a large mixing bowl, combine the melted butter, sugar, egg, egg yolk, milk and vanilla extract. Mix well until the ingredients are fully incorporated.
Add the gluten-free flour, almond flour, cocoa powder, salt, bicarbonate of soda and baking powder to the bowl. Mix the dry ingredients into the wet ingredients until a dough forms.
Reserve 30g of chocolate chips (just a small handful), and set aside for finishing the cookies after baking, then mix in the rest of the chocolate chips into the dough until evenly distributed.
Place the dough in the refrigerator for 2 hours, or overnight if desired. If chilling overnight, allow the dough to rest at room temperature for 10-15 minutes before proceeding, so it becomes slightly softened and easier to handle.
Pre-heat the oven to 190°C /170°C fan-assisted /325F / gas mark 5. Line a large baking tray with baking parchment paper.
Remove the dough from the refrigerator and roll the dough into equal sized balls, each weighing approximately 40g.
Place the cookies onto the prepared baking tray, spaced apart. You will have to bake the cookies in batches, 9-10 in each batch (or use 2 x baking trays).
Bake the cookies in the pre-heated oven for 10 minutes.
Once baked, remove the tray from the oven. While the cookies are still warm, you can use a large round cookie cutter to swirl around the cookies to gently coax them into perfect circles if you like. Press some of the extra chocolate chips into the tops of the cookies
You can sprinkle a small amount of flaked sea salt over each cookie if you want to.
Allow the cookies to cool on the tray for 10 minutes. Then transfer them to a wire rack to finish cooling completely.