Cocoa Sables

Mix flour, cocoa powder, and salt in a bowl and set aside.

Beat softened butter and sugar together with an electric mixer until the mixture looks like overwhipped whipped cream. Add egg yolk and vanilla extract; mix well. Add dry ingredients. Use a spatula to mix them in until evenly moistened.

Divide the dough into thirds or quarters and knead a little bit on a large sheet of waxed paper. Gather into a ball, then shape into a 1 1/2-inch cylinder or square tube. Wrap up with the waxed paper, pushing in the sides so that the tube is evenly thick from left to right. Repeat with remaining dough.

Refrigerate dough for at least 1 hour, and up to overnight.

Preheat the oven to 350 degrees F (175 degrees C). Line baking sheets with parchment paper.

Slice dough into 1/4-inch thick cookies with a sharp knife. Arrange on the baking sheets, spacing them 1/2 inch apart.

Bake in the preheated oven until firm, 20 to 25 minutes. Cool completely before eating.