Lemon Curd

from Martha Stewart Living | makes ¾ cup

1 large egg, plus 3 large egg yolks
1 ½ tsp. finely grated lemon zest
1/4 cup plus 2 Tbs freshly squeezed lemon juice (about 3 lemons)
1/2 cup sugar
pinch salt
2 oz (4 tablespoons) unsalted butter, cold, cut into pieces

1. Whisk together all ingredients except butter. Bring to a simmer in medium saucepan over medium heat, stirring constantly.

2. Cook until mixture is thickened, 4-5 minutes. Strain through a fine sieve into a bowl. Whisk in butter. Press plastic wrap directly onto surface of lemon curd and refrigerate until cold at least 1 hour or up to overnight.