Chocolate vanilla cookies

Ingredients
Butter 4 ounces
Caster sugar 4 ounces
Egg yolk 1
Vanilla essence 1 tsp
Flour 8 ounces
Baking powder 1 tsp leveled
Milk 2 tbsp
Coco powder 1 tbsp leveled
Egg white for brushing
Method
Sieve flour and baking powder, keep aside, beat butter gradually adding in caster sugar, add essence and egg yolk, fold in your sieved flour, knead with milk lightly, divide mixture in 2 portion add coco powder mixed with little milk in 1, put to chill for 30 minutes, roll each into rectangular, put on top of each other, cut with different shapes of cutter, put to bake on 180 degree C for 12 to 15 minutes, cool and use.