How to Make It
In a double boiler or a large heatproof bowl set over a saucepan with 1 inch of simmering water, whisk the lemon, grapefruit and orange juices with the eggs and sugar until combined. Cook, stirring constantly with a wooden spoon, until smooth and thick, 10 to 12 minutes; do not let the custard boil. Remove from the heat and stir in the butter.
Strain the custard into a bowl and stir in the grated citrus zests. Stir fro 1 minute to cool slightly, then cover with wax paper or plastic wrap and refrigerate overnight.
Spoon the citrus custard into shallow bowls or stemmed glasses and garnish with the fig wedges. Serve the custard with butter cookies.