Beat butter, cream cheese and sugar together until fluffy. Beat in the eggs one at a time, then add vanilla.
Mix in the flour mix and baking powder until smooth.
Divide dough, and add cocoa to one half. Mix well.
Between sheets of plastic wrap, roll out each portion of dough until it’s 1/4-inch thick.
Remove top sheet from each and lay the chocolate dough over the vanilla dough. Gently roll into a log, peeling away plastic wrap as you roll. Chill for 1 hour.
Cut into 1/4-inch slices, and place on a lined baking sheet. Bake at 350°F for 12 to 14 minutes or until edges are just slightly brown.