1. Preheat your oven to 180°C (160°C fan).

2. Grease and flour a 9-inch tart or cake tin that has a removable bottom. Line the bottom with a circular piece of baking paper.

3. Mix the flax seeds with 1 tablespoon of cold water and set aside for 5 minutes. It will thicken slightly.

4. In a large bowl, mix together the margarine, caster sugar and brown sugar. Stir in the vanilla extract and the flax seed mixture.

5. Add all of the flour and stir until it starts to stick together. Use your hands to press it into a ball of dough.

6. Gently knead in the chocolate chips.

7. Place the dough into the tin and press it out evenly, all the way to the edges.

8. Bake for 30-35 minutes until golden all over.

9. Leave it to sit in the tin for around 5 minutes or so then gently go around the edges with a butter knife to loosen the cookie from the tin. Use the removable bottom to lift the cookie out of the tin (leave the bottom on for now as the cookie will be quite fragile).

10. Transfer to a wire rack and leave to cool completely.

11. Once the cookie is cool, flip it over and carefully remove the bottom of the tin and the baking paper.

For the icing:

1. Mix the margarine, icing sugar and vanilla together. Add a splash of dairy-free milk if needed.

2. Stir in the food colouring(s), a little bit at a time until you get your desired colour.

3. Pipe the icing around the edges of the cookie. You can use any leftover icing to create a design in the middle.

4. Top with vegan sprinkles of choice.