Preheat your oven to 200°C/400°F (or 180°C/350°F if you're using a fan or convection oven). Have 2 large non-stick cookie trays to hand.

Mix the flax seeds with the water and set it aside to congeal. This will act as your flax "egg".

In a large bowl, cream together the margarine, the caster sugar and the brown sugar. Add the flax egg and the vanilla extract and mix it in.

Add the flour and the cinnamon and mix until the mixture starts to stick to itself. Then use your hands to press it into a dough. If it's too sticky, you can add a small amount of extra flour.

Add your chocolate chips and fold them into the cookie dough.

Divide the dough into 24 equal pieces; I used a scale to do this for accuracy. Roll each piece into a ball then flatten it slightly into a disc shape.

Place half of the discs onto your baking trays, leaving at least 2 inches of space between each one to allow for spreading.

Place around 1 teaspoon of Biscoff spread onto each cookie dough disc. Cover using the remaining cookie dough and seal them together at the edges by pressing down gently.

Bake for 10-12 minutes. 12 minutes will produce a slightly crunchy cookie and 10 minutes will produce a very soft cookie.

Let them cool slightly before removing them from the tray and enjoying. They will still be quite fragile while warm but will firm up as they cool.