Step 1 Whisk together eggs, yolk, sugar and salt. Whisk in citrus juice. Whisk in melted butter.
Step 2 Stove top method: Cook mixture in medium nonreactive saucepan over medium heat until it thickens, stirring constantly. Do not let mixture boil. Immediately strain through sieve into bowl. Cover with plastic wrap laid directly on surface and chill 1 hour.
Step 3Microwave method: Cook on high in 2-quart microwaveable bowl until curd thickens, 4 to 5 minutes, stirring every minute. Do not let mixture boil. Immediately strain through sieve into bowl. Cover with plastic wrap laid directly on surface and chill 1 hour.