Cookies: Preheat the oven to 350 degrees and position 2 racks in the upper and middle thirds of the oven. Cover 3 cookie sheets with parchment paper.
Sift cake flour, all-purpose flour, baking powder and salt into a mixing bowl or onto a large sheet of wax paper. In another large mixing bowl, beat butter and sugar at medium speed until light and fluffy, using a hand held electric mixer, about 3 minutes. Add eggs and yolks one at a time, beating well between additions. Add vanilla and milk to the mixture. At low speed, beat in the dry ingredients until JUST combined.
Spoon rounded tablespoons onto cookie sheets, about 2 inches apart. Bake for about 12 minutes, until the centers spring back when lightly pressed. Be careful not to brown or over bake, or they will be dry. Move the cookies, flat-side up, to a wire rack and let cool completely.
Icing: Meanwhile, in a medium bowl, whisk confectioners' sugar with the boiling water until smooth. Add vanilla and a few drops of food coloring. Whisk the mixture until color is even. Using a small offset spatula, spread the orange-colored icing over half of the flat side of each cookie. You will have orange icing left over (for next step).
In your microwave, melt the chocolate in a small bowl or glass measuring cup. Stir melted chocolate into the left over orange icing. Spread the chocolate icing on the other half and let stand until set, about 15 minutes. (If the icing becomes too thick, add hot water, 1 teaspoon at a time, until smooth and shiny.).