Preheat your oven to 180℃ or 350℉ (160℃ or 325℉ for fan/convection ovens).

Line a large baking tray or two with baking paper.

Mix the flax seeds and water together and leave it to sit at room temperature for around 5 minutes until thick and gloopy. Set aside for now- this will be your flax 'egg'.

In a large bowl, mix together the margarine, caster sugar and brown sugar. Once smooth, add in your flax egg and the vanilla extract. Mix well.

Now add all of the self-raising flour and stir it in. When the mixture is starting to stick together, use your hands to press it into a ball of dough. If the dough is too wet, add more flour and if it's too dry, add a splash of milk.

Add in the chocolate chunks and gently knead them into the dough with your hands.

Divide the dough into 12 equal-sized pieces and roll into balls. Gently flatten them with your fingers until around 1-inch thick.

Place them on the tray, leaving a few inches of space in between to allow for spreading. I typically bake 5 per tray at a time.

Bake for 10-12 minutes until the cookies are just turning slightly golden brown at the edges. They'll look a bit underdone when you take them out but will become firm and chewy once cooled. Don't continue baking or they'll end up hard and crispy.

Sprinkle with sea salt while the cookies are still warm.

Let the cookies cool completely before taking them off the tray then enjoy!