Here is the recipe
1¼ cups all-purpose flour
1/3 cup unsweetened cocoa powder
½ tsp baking soda
155g unsalted butter, at room temperature
2/3 cup (packed) light brown sugar
¼ cup sugar
½ tsp fleur de sel or ¼ tsp fine sea salt
1 tsp pure vanilla extract
140g bittersweet chocolate, chopped into chips, or a generous ¾ cup mini chocolate chips
Sift the flour, cocoa and baking powder together.Beat the butter until soft and creamy.Add both sugars, the salt and vanilla extract and beat for 2 minutes more.
Pour in the dry ingredients and mix just until the flour disappears into the dough- for the best texture, work the dough as little as possible once the flour is added, and don’t be concerned if the dough looks a little crumbly.
Toss in the chocolate pieces and mix only to incorporate.Turn the dough out onto t a work surface, gather it together and divide it in half.Working with one half at a time, shape the dough into logs that are 4cm in diameter.
Wrap the logs in plastic wrap and refrigerate them for at least 3 hours. (The dough can be refrigerated for up to 3 days or frozen for up to 2 months. If you’ve frozen the dough, you needn’t defrost it before making- bake for 1 minute longer.)
Preheat oven to 160˚C.Line two baking sheets with parchment paper or silicone mats.Using a sharp knife, slice the logs into rounds that are 1 cm thick. Yikes.. don't slice it on your silicone mat, or you'll have a shreded mat!
(The rounds are likely to crack as you’re cutting them- don’t be concerned, just squeeze the bits back onto each cookie.)Arrange the rounds on the baking sheets, leaving about 3cm between them.Bake the cookies on sheet at a time for 12 minutes- they won’t look done, nor will they be firm, but that’s just the way they should be.Transfer the baking sheet to a cooling rack and the cookies rest until they are only just warm, at which point you can serve them or let them reach room temperature.
STORING: Packed airtight, the cookies will keep at room temperature for up to 3 days; they can be frozen for up to 2 months.