I have a recipe from Preserving by Oded Schwartz. It can be used for toast and such, but also for filling pastries and cakes.
For 2 pints
Grated rind and juice of 1 grapefruit
Segmented flesh of 1 grapefruit
juice of 2 lemons
1 1/2 cup sugar
7 T butter softened
4 eggs and 2 egg yolks beaten
3 T orange-flower water
Place the grapefruit rind, juice, and flesh , the lemon jiuce, and sugar in a small pan. Heat gently, stirring until the sugar is dissolved. Add the butter and stir until melted.
Transfer the mixture to the double boiler or a bowl place over a pan of simmering water, Strain in the eggs and cook over barely simmering water, stirring often, for 25-340 minutes, until the mixture coats a the back of a spoon. Do not let it boil or it will curdle. Remove from the heat and stir in the orange flower water. Pour the curd in the warm and sterilized jars and seal.