Combine whole eggs, yolks, sugar, salt, and lemon zest in a medium pot, then whisk in lemon juice.
Cook over low heat, stirring constantly but not vigorously, until warm to the touch, about 3 minutes.
Increase heat to medium-low and continue cooking and stirring until thick and steaming-hot (custard should register 170°F on an instant-read thermometer), about 8 minutes.
Immediately strain into a bowl and let cool. Can be made ahead and placed in the refridgerator until ready to use.
Meringue shells:
Preheat your oven to 250 degrees F and place the oven rack in the center of the oven. Line a baking sheet with parchment paper and draw 8 - 4 inch circles on the paper. Turn the parchment paper over so the circles are on the reverse side.
In the bowl of your electric stand mixer, fitted with the whisk attachment (or with a hand mixer), beat the egg whites and cream of tartar on medium low speed until they hold soft peaks. Start adding the sugar, a tablespoon at a time, and continue to beat, on high speed, until the meringue holds very stiff and shiny peaks. Beat in the vanilla extract. Sprinkle the vinegar and cornstarch over the top of the meringue and, with a rubber spatula, gently fold in.
Place the meringue in a piping bag with your desired tip and create nests using the circles as your outline. Start by piping a dot in the centre of your meringue nest, then in one continuous motion go around the dot to make a bigger circle, and then go around again on top of the outer circle to make the sides. You can also use a spoon to form nests into the circles.
Bake for about 45 minutes or until the outside is dry and crisp. Turn the oven off, leave the oven door slightly ajar, and let the meringues cool completely in the oven (a couple of hours).
The cooled meringues can be made and stored in an airtight container in a cool dry place, or in the refrigerator, for a few days.
Assembly:
Place a few tablespoons of lemon curd in the middle of each nest and topped with whipped cream. Enjoy immediately!