Whisk yolks and eggs in medium bowl to blend. Set aside.
Combine lemon juice, butter, and sugar in large metal bowl. Set bowl over saucepan of simmering water; whisk until butter melts and sugar dissolves.
Gradually whisk 1/3 of hot butter mixture into eggs, whisk mixture back into bowl with remaining butter mixture set over simmering water. Whisk constantly until custard thickens and thermometer inserted into mixture registers 180° F, about 5 minutes (do not boil). (If you don’t have a candy thermometer, wait until the mixture thickens and coats the back of a wooden spoon.)
Pour lemon curd through strainer set over medium bowl. Place plastic wrap directly on surface of lemon curd; chill overnight.
Can be made up to 1 week ahead. Keep refrigerated.
This recipe will make more lemon curd than you need for the tiramisu. Package it in a pretty jar as a gift, or keep it for yourself to eat with biscuits, scones, or crackers.
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