Mix juice, zest, salt, sugar, butter, egg yolks and eggs in a medium metal bowl.

Place over a saucepan a third of the way full of simmering water.

Cook lemon mixture in the bowl over simmering water, whisking the whole time until the mixture has thickened and a trail forms through the curd with the whisk, about 10-15 minutes.

Strain through a fine mesh sieve, and pour directly into the prebaked tart shell.

Press plastic wrap to the surface and set in the refrigerator to chill.

Using the bowl of a stand mixer, whisk together egg whites, sugar, and salt. Place over a simmering saucepan of water whisking very quickly the whole time, and warm the egg white mixture until the sugar is dissolved and the mixture is very warm to the touch.

Pull off the heat, and using a whisk attachment on the stand mixer, whip the egg white mixture until stiff peaks form.

Preheat oven on broiler setting and place oven rack close to the top of the oven.

Portion meringue over the cooled lemon curd in the tart shell, and spread evenly over using a spatula or the back of a spoon.

Place the tart in the oven and toast the meringue for a minute using the broiler, making sure to rotate and keep a close eye out.

Slice and serve!