Double Chocolate Cookies

1 cup (140g) all-purpose flour
½ cup (45g) unsweetened Dutch-process cocoa powder
½ teaspoon baking soda
½ teaspoon coarse salt – I used Maldon
224g (½ pound) good-quality milk chocolate, 112g (4 ounces) coarsely chopped and 112g (4 ounces) cut into 0.60cm (¼-in) chunks
½ cup (113g/1 stick) unsalted butter
1½ cups (300g) sugar
2 large eggs
1 teaspoon pure vanilla extract

Preheat oven to 165°C/325°F. Whisk together flour, cocoa powder, baking soda, and salt; set aside. Melt 112g (4 ounces) coarsely chopped chocolate with the butter in a small heatproof bowl set over a pan of simmering water; let cool slightly.
Put chocolate mixture, sugar, eggs, and vanilla in the bowl of an electric mixer fitted with the paddle attachment. Mix on medium speed until combined. Reduce speed to low; gradually mix in flour mixture. Fold in chocolate chunks.
Using a 1 ½-inch ice cream scoop, drop dough onto parchment-lined baking sheets, spacing 5cm (2 inches) apart. Bake until cookies are flat and surfaces crack, about 15 minutes (cookies should be soft). Let cool on parchment on wire racks. Cookies can be stored between layers of parchment in airtight containers at room temperature up to 3 days.