Whisk sugar, eggs, egg yolks, lemon juice, and zest in a saucepan until smooth.

Cook over medium-low heat, whisking constantly, until the curd thickens enough to coat the back of a spoon and holds a line when you run a finger through it, 6 to 8 minutes.

Remove from heat and whisk in the cold butter, one cube at a time, until the curd is glossy and smooth.

Strain the curd through a fine sieve into a bowl, press plastic wrap directly onto the surface, and refrigerate for 1 hour, until fully chilled and set.

Spoon the chilled curd into the cooled tart shells, filling each almost to the top and smoothing with the back of the spoon.

Whip heavy cream and powdered sugar to soft peaks, about 2 minutes.

Pipe a small rosette of whipped cream onto the edge of each tart.

Finish each tart with a sugared lemon zest strip and a small piece of gold leaf just before serving.