Let cool completely before crushing for tart base.
Crush the baked biscuits (should yield about 120–150g crumbs).
Mix with 60g melted butter.
Press into tart case(s), chill until firm.
Crush the biscuits
Use a food processor or bash in a bag with a rolling pin until fine crumbs.
Mix with melted butter. Stir until the texture resembles damp sand. Add any extras (zest, spice) if using.