Preheat oven to 180ºC. Line a baking tray with grease-proof paper.
In a bowl, or the base of your stand mixer, add butter and sugar. Beat until light and creamy. Add the tahini, egg and vanilla extract and beat again until combined - approximately two minutes.
Add both flours, baking powder and salt and fold into wet ingredients with a spatula. Add sprinkles and mix in until distributed evenly.
Using an ice cream scoop, or a quarter cup, scoop out cookie dough, form into balls and press down lightly on to the tray. Repeat with remaining mixture.
Bake for 9 minutes for a cookie that is crunch around the outside and chewy in the centre. Allow to cool before eating.