Soften the butter, add to a large mixing bowl and beat with the sugar and vanilla essence until light and fluffy
Add the egg to the mixing bowl and beat until combined
Sift the flour and cocoa and add to the mixing bowl, beat until combined
Add the white chocolate to the mixing bowl and fold until combined
Roll the mixture into tablespoon sized balls and place on the baking trays, press them down gently. Leave a space for the cookies to spread as they cook
Bake in the oven for 12-15 minutes, remove the trays from the oven and allow the cookies to settle on the trays for 1-2 minutes. Remove the cookies and allow to completely cool on a wire rack