CUPCAKES: Preheat oven to 325 degrees. In a large mixing bowl, mix flour, salt, baking powder, baking soda and sugar together. Add butter and milk and mix at medium speed for 2 minutes. Add eggs and vanilla and beat 2 more minutes.
Divide the batter in half, and mix coffee and cocoa powder into one half of the batter, mixing well for 2 minutes to incorporate. (using two pyrex measuring cups or containers with spouts works well for this).
Using both hands, pour equally and at the same time both batters into lined muffin tins so that they fill each cup equally side by side (it helps if you have a helper nearby).
Carefully place muffin pan into the oven and bake for approximately 20-25 minutes or until toothpick comes out clean. Cool completely on cooling racks.
MAKE THE FROSTING: Place butter and confectioners sugar in a bowl and beat until creamy. Blend in half and half and vanilla.
Divide the icing and mix cocoa powder into one half, mixing well. Frost a yin-yang design over top in opposing color of each side of the muffin (white frosting on chocolate side, chocolate frosting on white side).