1: Spread 200 g sweetcrust pastry (pâte sablée) lengthwise, not too thinly (you need a nice crust after baking) and pour the pan. I'm using a full-length pie tin here, but if you don't have one, a cake tin will do, just leave only 2 cm or 1 inch of pastry height around the edges. Put on standby in the fridge, leaving the pastry sticking out well as in the photo (important).
3: Then add 2 egg whites and mix with soft spatula or wooden spatula until obtain a soft mix. Because egg whites can differ in volume or weight, I advise you to add 1 first and mix, and then add remaining egg white in stages until getting the required soft texture.
4: You can add green 3 drops food colouring, but it is not necessary.
5: Take the tin out of the fridge, and trim the excess pastry all around.
6: Spread mixture in pastry case.
7: Bake for about 30 minutes.
8: Allow to cool on a rack, then sprinkle with ice sugar. Serve in fairly thin slices.
Remarks
It's best to allow the cake to cool in the tin, and then turn out and leave on a wire rack until cold.