1. Chop 8 ounces of milk chocolate and semisweet/bittersweet chocolate in small pieces and place in a bowl large enough to hold whipping cream. Set aside.
2. In a saucepan bring whipping cream, sugar, and zest to a boil. Remove from heat and pour onto chopped chocolate.
3. Set aside until mixture has firmed and holds its shape, about 4 hours or preferably overnight.

To prepare truffles:

1. On a plastic food film lined cutting board, use a 2 teaspoon melon baller to scoop out mounds, or pipe mixture into a ball shape using a piping bag with a plain round tip.
2. Using your hands roll in a perfect ball shape. It's best to use gloves to keep filling from warming up in your hands. If filling becomes too soft, place briefly in the refrigerator to firm.
3. Chop 12 ounces of milk chocolate and place in a microwave-proof bowl.
4. Heat in 8-10 second increments until about half of chocolate is melted. Continue to heat in 5-6 second increments until about 3/4 of chocolate is melted. Without further heating, stir chocolate until nearly melted, but a few lumps are okay.
5. Place a small amount of melted milk chocolate in the palm of your hands and roll a truffle in it to coat well. Place coated truffle on a plastic food film lined counter until hardened.
6. If exterior milk chocolate becomes too firm, heat in the microwave for 5-6 seconds and stir well until smooth.
7. Top with a bit of fresh lime zest, if desired. 
8. Keep truffles refrigerated.