Preheat oven to 180 degrees. Line a baking tray and set aside.

Beat butter and sugar till fluffy. Add the vanilla and beat.

Sift in the flour and cocoa powder into the mixture, add the salt and fold in till all covered.

Scoop out small balls and plop onto the baking tray. Flatten with a spoon or a fork on the top.

Bake for around 10 minutes, just till set. Allow it to cool on the rack till hardened.