Melt butter for the bottom. Finely grind the speculoos, lady fingers and 50 g walnuts. Mix with the fat. Spread the bottom of a springform pan (24 cm Ø) with oil, spread the mixture in it and press it down firmly. Pull up the rim a little and put it in a cool place for about 1 hour. For the cream pour milk and whipped cream into a mixing bowl.
Add cream powder while stirring. Whisk at highest setting for 3 minutes with the whisk of the hand mixer. Spread on the cake base and chill for another hour. To decorate, peel the grapefruit so that the white skin is completely removed. Cut one fruit into slices. From the second fruit, cut out fillets between the parting skins. Knead marzipan and icing sugar. Divide into 3 pieces and colour as desired. Roll out thinly between 2 layers of cling film and cut out stars. Roll them in sugar. Chop 25 g walnuts.
From the second fruit, cut out fillets between the parting skins. Knead marzipan and icing sugar. Divide into 3 pieces and colour as desired. Roll out thinly between 2 layers of cling film and cut out stars. Roll them in sugar. Chop 25 g walnuts. Decorate the cake shortly before serving with prepared grapefruits, stars and walnuts. Makes about 12 pieces