Add the flour, sugar and vegan butter to a large bowl. Rub in the butter with your fingertips or a fork until the mixture is crumbly.

Sift in the cocoa powder and add the vanilla. Mix until a dough is formed. Avoid overmixing.

Add the dough to a clean surface or cutting board. Roll and shape it into a 10-inch log.

Wrap the dough tightly in a large sheet of plastic wrap and chill for at least 1 hour or until firm in the fridge. Store the dough in a cutout paper towel tube to help keep its rounded shape.

Arrange two oven racks just above and below the middle rack position. Preheat the oven to 350°F (180°C) and line two baking trays with parchment paper.

Unwrap the dough on a cutting surface. Slice off the ends to make them neater, using a sharp, straight-edged knife and a slicing (not sawing) motion.

Mark and cut the remaining dough into 17 half-inch or 34 quarter-inch slices. Arrange the rounds at least 1 inch apart on a baking sheet lined with parchment paper.

Bake thinner cookies for 15 to 20 minutes and thicker cookies for 25 to 30 minutes. Rotate the cookie sheets and switch them on the shelves halfway through baking. Add more time to make the cookies more crisp, if desired.

Cool the cookies on the trays for 5 minutes before transferring them to a cooling rack.