Preheat oven to 220°C/430°F and grease a 16cm cast iron skillet (or shallow cake pan).
Prepare your flax egg by mixing the flax seeds with 2 tablespoons of water and set aside to thicken.
In a large bowl, mix together the melted butter, brown sugar, and caster sugar. Add the vanilla and flax chia egg.
Add the flour and baking soda and gently combine to form a sticky dough.
Fold in the chocolate chips and cover the bowl with cling film. Freeze for 20 minutes.
Place the chilled dough into the center of the skillet and press gently with your fingers until it almost reaches the edges. (it will spread slightly in the oven)
Bake for 10-12 minutes. It will be golden brown on top and gooey inside.
While the cookie dough is baking, prepare your chocolate sauce by mixing the cocoa powder and agave nectar together. Add a splash of water to thin it out if desired.
Leave your cookie dough to stand for 5 minutes before enjoying it warm with ice cream and chocolate sauce.
Best served warm, fresh from the oven