Simmer the grapefruit juice in a small saucepan, reducing to 1/2 cup / 120 ml. Let it cool a bit.
Cream the butter in a medium stainless steel bowl (note: you'll use this bowl as a makeshift double-boiler later). Add the sugar and beat until fluffy and light. Add the yolks, and then the eggs one at a time, beating well to incorporate after each addition. Stir in the salt, and then gradually add the grapefruit juice, lemon juice, and ginger juice - working the juice in as you go.
Rinse out the small saucepan you used earlier, and fill 1/3 of the way full with water. Bring to a simmer, and place your stainless steel bowl of curd on top of it. Stir constantly, and heat the curd slowly enough that the sugar (if you used it) has time to dissolve. This step usually takes me about ten minutes. Pull the curd from the heat when it is just thick enough to coat your spoon, around 166 degrees, F. Your curd will thick substantially as it cools. It's wonderful warm or cool.
|Basic biscuit topped with cinnamon and curd|