In a large bowl, blend the butter and sugar for 4 to 5 minutes until creamy. Add egg yolk and Vanilla extract and mix until well combined

Add the floor and salt and using a spatula bring the dough together Wrap vanilla dough in a plastic wrap and shape into a rectangle. Refrigerate the dough for 2 hours

In another large bowl, blend the butter and sugar for 4 to 5 minutes until creamy, add egg yolk and mix until well combined. Add flour, cocoa powder and salt mix everything well together. Wrap chocolate dough in plastic wrap. Shape like rectangle. Refrigerate for 2 hours

Preheat the oven to 180 degree and line the baking tray with parchment paper

Slice the log into 1/4 inch thick cookies, place the cookies on the prepared baking sheet with a gap between them

Bake cookies for 12 to 14 minutes until the edges are golden brown

Allow the cookies to cool for 10 to 15 minutes on the baking sheet,now cool completely on the wire rack. Store in airtight container. Serve with cup of warm milk