Whisk the whole eggs vigorously with the powdered sugar in a large bowl or in a bowl. Stop when the mixture has whitened and turned frothy.
Add the juice and grated zest of the lemons as well as the melted butter and the cornstarch (cornstarch) diluted in a tablespoon of water. Mix.
Line a pie dish with a sheet of baking paper and the shortbread dough. Use your fingers to adhere the dough to the edges of the mold and prick it with a fork. Pour the lemon cream directly on the pie and bake 35 to 40 minutes at 180 ° c (thermostat 6) until the cream is set and golden on top. Let cool to room temperature.
While the pie is baking and cooling, whip the egg whites to stiff peaks with a pinch of salt. When the whites start to rise, add the icing sugar in two steps: a tablespoon of sugar when the whites start to rise, then the rest at maximum speed to tighten them.
Once the pie has cooled, garnish it with the meringue, distributing it evenly with a spatula. Decorate the pie by dipping a whisk in the meringue and then lifting it quickly to form wedges. Cook for a few moments under the grill of a very hot oven, taking care not to let the meringue burn.