Tip the butter and sugar into a large bowl and beat until light and fluffy.
Mix the flour, salt, cumin seeds and baking powder together, then tip into the creamed butter and sugar mixture. Mix to combine, gently bringing the dough together without over working it. Form into a log shape, about 5cm in diameter, and wrap in cling film. Place in the fridge for 30 minutes.
Heat the oven to 200°C/Fan 180°C/Gas 6. Line a large baking sheet with baking parchment.
Remove the dough from the fridge, slice into discs, about 7–8mm thick, and lay on the lined baking sheet. Bake for 15–18 minutes, or until golden brown and cooked through.
Transfer the biscuits to a wire rack and leave to cool. They will keep in an airtight container for up to 2 days.