Sift flour, cocoa powder and baking soda into a large bowl. Add salt and whisk to blend evenly.

Combine soft butter with brown sugar in a large bowl and beat with a wide spatula until pale and creamy. It should be lightened and fluffy-looking. Mix in egg yolk and vanilla.

Scrape down the sides of the bowl and add the flour mixture. Fold it in until combined.

Add chopped pistachios and dark chocolate and fold them through so they are evenly incorporated.

Bring the dough together with your hands and then roll into a long log about 12 inches long. If you are rolling in pistachios, sprinkle ground pistachios on your surface and place the dough log on top. Roll the log back and forth while applying some pressure so the pistachios adhere to the log.

Wrap the dough log in plastic wrap tightly and place in the fridge for 1-2 hours (or in the freezer for baking at another time).

When ready to bake, preheat your oven to 350°F and line two large cookie sheets with parchment paper.

When ready to bake, slice the log into ½ inch coins. If some of the chocolate chunks in the cookie dough are large, they will be very hard and may not slice neatly, leaving gaps in some cookies. To correct this, just press the dough together with your fingers to shape it back into a circle.

Place cookie dough slices on your prepared baking sheets with about 2 inches of space between them and bake for 10-12 minutes.

Let cookies cool on the trays for a few minutes before using a spatula to help to transfer them to a wire rack to finish cooling. Once cool, drizzle with extra melted chocolate and sprinkle with crushed pistachios.