Preheat your air fryer to 340F or your oven to 350F.
In a bowl, place your dark chocolate and butter together and microwave in intervals of 20 seconds until melted, making sure to stir occasionally.
In a separate bowl, combine your sugars and egg and whisk vigorously until light and fluffy (3 to 5 minutes). Pinch the mixture between your fingers and if you feel a lot of granules, keep mixing, you want most of your sugar to dissolve.
Add vanilla and mix until combined.
Add your melted chocolate and butter and mix to combine.
Add your dry ingredients except for your chopped chocolate or chips and fold to combine.
Once combined, fold in your chocolate.
In 2 parchment lined dishes, evenly divide your batter between before placing them in your air fryer and baking for about 10 to 20 minutes or until a tooth pick comes out relatively clean (moist crumbs are okay, you don't want obvious signs of wet batter).
If using an oven, bake for 20 to 25 minutes.
