Mix the flaxseeds with 2 tablespoons water and set aside for 3-5 minutes. This will be your egg replacement, also known as a "flax egg".

Melt the butter, then add the brown sugar, caster sugar and vanilla. Add the flax egg and combine everything using a wooden spoon.

Add the flour and baking powder to the bowl and mix to form a very sticky dough.

Fold in the chocolate chips/chunks, then freeze the dough for 30 minutes. Preheat oven to 180C/350F and line a tray with baking paper in the meantime.

Once the dough has chilled, scoop 1 tablespoon at a time onto the tray, leaving about 2 inches between each cookie ball. 

Slightly flatten the balls using your hands then bake for 15-20 minutes. 15 minutes makes soft, chewy cookies. The longer you bake, the crunchier they will become.

Leave the cookies to cool completely before removing them from the tray. 

Place the butter, sugar, and vanilla into a pan and turn the heat to medium-high. 

Once the butter has melted completely, set a timer for 2 minutes and stir continuously until the timer goes. Remove from the heat and leave to cool for a few minutes.

Spoon 1/2 a tablespoon of toffee onto the center of each cookie and sprinkle with sea salt. Work quickly to prevent the toffee setting in the pan.

Allow the toffee to cool completely (at least 30 minutes) before eating the cookies.