1. Position your oven racks so that one is in the center, and preheat the oven to 350 degrees.
2. Whisk the eggs and yolks together in a medium-size bowl. Add the sugar with one hand while continuing to whisk with the other. Still whisking, pour in the lemon zest and juice, then the cream. Pour this lemon custard into your par-baked tart shell. It should come to 1/8 inch from the top edge of the tart. You may have leftover custard, which you can bake in a small ramekin—a little treat for yourself.
3. Place the tart on the center rack in the oven, taking care not to spill the custard, and bake the tart for 25–30 minutes, or until filling is firm to the touch and doesn’t jiggle when you shake the pan.
4. Remove the tart from the oven, and set it on a wire rack to cool slightly.
5. To remove the tart from the pan, rest it on a big can. Make sure the tart is steady and balanced. Slide the outside ring of the pan down off the tart. Move the tart to your work surface, and slide the tart off the pan bottom onto a rimless serving dish or a cutting board. Serve at room temperature or chilled.