In the bowl of a stand mixer or a mixing bowl with a hand-held mixer, beat the butter and granulated sugar on medium speed until well blended, about 2 minutes.

Add the eggs, one at a time, beating each until fully incorporated before adding the next.

Slowly add the lemon juice to the butter mixture while beating on low speed just until blended.

Remove the bowl from the mixer and stir in the lemon zest by hand. The mixture may look curdled, but that is normal.

Pour the mixture into a small, heavy-bottomed stainless steel saucepan.

Cook over medium-low heat, whisking constantly, until the mixture thickens and coats the back of a spoon, about 14 to 16 minutes. Avoid using a reactive metal whisk, as it may interact with the acidity of the curd.

Transfer the lemon curd to a heat-safe bowl. While still warm, place a piece of plastic wrap directly on the surface of the curd to prevent a skin from forming.

Chill in the refrigerator for at least 2 hours, or until firm.

Store the lemon curd in an airtight container in the refrigerator for up to 2 weeks.