Preheat the oven to 180°C and line a large baking tray with a sheet of baking parchment paper.
Mix the butter, sugar and tahini until pale and fluffy. Then mix in the lemon zest and lemon juice. Fold the flour and the baking powder in the wet ingredients and stir gently to combine.
Roll out about 20 balls from the mixture and space them apart on the baking tray. Press them with your fingers to make them flat and roll the sides of the mixture into a bowl with black and white sesame seeds.
Bake for 14-16 minutes until the edges are golden brown. Let them cool and enjoy!