In a 2 quart saucepan whisk together
1/2 Cup fresh lemon juice
2 tsp. finely grated fresh lemon zest
1/2 Cup sugar
3 large eggs
Stir in
6 Tbs unsalted butter cut into small pieces
Cook over moderately low heat, whisking frequently, until curd is thick enough to hold the marks of the whisk
When the first bubble appears on surface, about 6 minutes; remove from heat immediately
Transfer lemon curd to a covered bowl and chill until cold, at least 1 hour
Curd can be chilled up to 1 week.