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Beat butter and sugar in stand mixer until blended. Add eggs and egg yolks, 1 at a time, beating just until blended after each addition.
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Gradually add lemon juice to butter mixture and beat until blended.
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Stir in zest
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Transfer mixture to a heavy 4-quart saucepan and cook, whisking constantly over medium heat until mixture thickens and easily coats the back of a spoon, about 14 minutes.
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Chill untli firm (about 4 hours).Refrigerate in an airtight container up to 2 weeks.