intensely chocolate sables

Name: intensely chocolate sables
Cuisine: European
Ingredients: 1 cup (125 grams) all-purpose flour; 1/3 cup (30 grams) Dutched cocoa powder (see Updated Note); 1/4 teaspoon baking soda; 1/2 cup (1 stick, 4 ounces or 115 grams) unsalted butter, at room temperature; 1/2 to 2/3 cup (100 to 135 grams) granulated sugar (less for a more bittersweet cookie); 1/4 teaspoon fine sea salt; 1 large egg yolk; 1/2 teaspoon vanilla extract; 3 1/2 ounces (100 grams) semi- or bittersweet chocolate, grated or finely chopped until almost powdery in a food processor; Coarse sugar (turbinato/sugar in the raw or decorative) for sprinkling