Cream the butter and sugar. Add eggs, cream/milk, and vanilla. Mix thoroughly.
For plain recipe: Combine flour with salt and baking powder and add it to the wet mixture, stirring thoroughly.
For Chocolate recipe: Combine the flour with the salt, baking powder, and cocoa powder and add it to the wet mixture, stirring thoroughly.
Note: If the mixture seems to get dry (crumbly), sprinkle a little water over the dough (wet your fingers and flick the water on the dry spots) and continue to mix until dough is uniformly moist and pliable (not sticky).
Turn the dough onto a floured surface (wax paper) and work it into a smooth ball— knead it so there will be no fissures within it, but don't dry it out. Then proceed to shape it into a long cylinder, about 2 inches in diameter. Once you have two cylinders (one each flavor) of the same diameter and length, cut them into three paired, equal and matching sections and begin shaping...
Working with cylinder pairs, and placing each on a clean sheet of waxed paper (flour won't be needed now), what you want to do is flatten one side of each cylinder so that, in cross-section, it takes on a teardrop shape— and be sure to keep the edges "squared-up." Then, using the side of your hand, squash down the tail end of that teardrop so it resembles the familiar "circle with a tail" in cross-section— and be sure to keep the edge "squared-up" and as uniformly smooth as possible— touch it up slightly with a wooden dowel if you've got one.
When you have both pieces shaped, moisten the shaped side of one piece with water. Position the other section on top to form a cylinder. Pat and stroke the dough and roll it gently back and forth to be sure the sections are adhering— you should have nice straight seams top and bottom and be able to see the yin-yang shape when you look at the end.
Roll the cylinder up in waxed paper and place it in the refrigerator to chill thoroughly (over night, if you like)— and be sure rest it so that you can see the "seam" on top.
When the dough is cold through, use a sharp knife and cut 1/4 inch slices. Shape the slices into more perfect rounds, and place them on a baking sheet leaving about an inch between them for expansion— unless you want to try for the eight-sided "bagua" effect you'll get if they "run" together!— and alternating rotation directions. Press semisweet chocolate and white chocolate bits into appropriate positions.
