Whisk together the flours, cocoa, baking powder and salt in a medium bowl.
Using an electric mixer, beat the butter and sugars in a large bowl until creamy. Beat in the egg,milk and vanilla.
With the mixers on low speed, mix in the flour mixture until blended and the dough starts to clump together.
Gather the dough into a ball, cover with a plastic wrap and refrigerate for an hour.
Preheat the oven to 350 degree Fahrenheit. Line 2 cookie sheets with parchment paper.
Pinch off clumps of dough and form into 1" inch balls and place them on the sheet around 2" inches apart. With the heels of your hand flatten the balls to around 1/2"inch thickness.
Bake for 13 to 14 minutes. Transfer to a wire rack to cool completely.