In a medium bowl, whisk granulated sugar, eggs, egg yolks, and grapefruit zest.*

In a medium saucepan, warm the grapefruit and lemon juices until steaming. Do not boil.

Temper** the hot juice into the egg yolk mixture, adding a small amount at a time and whisking well after each addition, until you’ve incorporated all of the juice.

Return mixture to saucepan and cook over medium-low heat. Bring to a low boil and continue cooking until thickened, about 4 minutes. While cooking, continually stir the curd with a whisk or rubber spatula.

Remove from heat. Whisk in the butter and gel food coloring, if using.

Pour curd into a clean bowl. Cover with clingfilm/plastic wrap, allowing the plastic to touch the top of the curd to prevent a tough skin from forming.

Refrigerate until ready to use. Before serving, use a wire whisk to ‘knock back’ the curd, whisking for 1-2 minutes or until smooth and creamy.

Store grapefruit curd in an airtight container in the refrigerator for up to 3 days.