Preheat the oven to 160°C. Line a 25 x 25cm baking tin with baking paper.
Melt the coconut oil or butter with the chocolate in a pan on a low heat. Remove from the heat and leave to cool slightly.
Beat the sugar, vanilla and eggs together until combined. Once the chocolate has cooled a little, pour it into the egg and sugar mix. Sift in the flour and a pinch of salt, stirring well then add in the tahini.
Pour the mix into the baking tin and scatter over some sea salt flakes (about ¼-½ tsp) and sesame seeds. Bake for 25-30 minutes until the brownie is just set – you want the outside to be crispy and the centre nice and gooey. Remove from the oven and leave to cool in the tin. Once cool, cut into squares.
They will last for 1 week in an airtight container in a cupboard.