Mix the flour, baking powder, caster sugar, orange zest and a pinch of salt. Whisk the eggs, vanilla extract and tahini together until frothy then stir into the flour mixture. Pour in the cooled melted butter and stir to combine. Transfer to a piping bag and chill overnight.
When you’re ready to cook the madeleines, preheat the oven to 170°C, gas mark 3. Oil a madeleine tray with baking spray and pipe a line of mix into each hole.
Bake for 8-10 minutes, or until golden. Leave to cool slightly in the tray then transfer to a wire rack until completely cool. Decorate with white chocolate, pistachios and orange zest.