Melt-in-your-mouth chocolate shortbread cookies

Separate the egg whites from the yolks at 1 egg.

In the bowl of a mixer, combine 85 g icing sugar, 170 g butter, 15 g powdered cocoa, and 2 pinches fine (or table) salt.

Turn on the mixer at a medium-low speed until the mixture is creamy and chocolatey.

Turn off the mixer, add the egg yolk and 210 g flour, then turn it back on at low speed...

...until the mixture is smooth.

Pour the dough onto your work surface, and shape it into a large ball.

Cut the ball in half, then roll each half into a cylindrical log about 3 cm (1.2 inch) in diameter.

This isn't easy because the dough is very soft, but you can refine the shape in the next step.

Wrap each cylinder, and once you've done that, it'll be easier to roll them more carefully.

Put them in the fridge for 1 to 2 hours, or even overnight.

After that time has elapsed, preheat your oven to 160°C (320°F).

Remove the plastic wrap from one of the cylinders—which has become quite hard after being in the fridge—and use a pastry brush to coat its entire surface with egg white.

Then sprinkle it with 4 tablespoons granulated sugar.

Then cut it into slices about 1 cm (0.4 inches) thick.

The thin layer of granulated sugar on the slice gives it a shiny appearance known as a “diamond.”

Do the same for the other cylinder, and place the slices on a sheet of parchment paper laid out on a baking sheet.

Bake for 12 minutes.

Let them cool on a wire rack.

Your melt-in-your-mouth chocolate shortbread cookies are ready to enjoy.