6 large egg yolks (room temperature)
1/2 cup minus 2 tsp granulated sugar**
generous pinch kosher salt
1/2 cup fresh grapefruit juice
zest from a large grapefruit
2 tsp fresh lemon juice (do not use meyer lemon)
1/2 cup unsalted butter--cut into small pieces
whisk egg yolks, sugar, and salt until the eggs are lemon yellow and thick. Whisk in zest and juices. Prepare a bain marie or double boiler. Place eggs mixure in a bowl over double boiler. Cook while constantly stirring being careful not to overcook. The curd should be thickened and coat the spoon. It will continue to thicken up as it cools. Pass through a sieve into a clean bowl. While it is still warm, stir in the butter pieces and stir until it is completely melted and incorporated. Cover with plastic wrap, pressing down on top to avoid a skin forming. Refrigerate until ready to use. The curd will firm up in the fridge, but it is a soft curd, that is best used as a spread or a sauce.
**the sweetness of your curd depends on the sweetness of the grapefruit. If you find your grapefruit to be really sweet, adjust the sugar level, if you find it really sour or bitter, adjust accordingly as well.