Preheat oven to 350 degrees F. Line two baking sheets with foil or parchment paper.

In a large bowl, stir together the cookie mix, butter, lemon zest, vanilla, eggs and buttermilk until smooth.

Using a heaping tablespoon, drop batter onto baking sheet spacing a few inches apart. I only did 6 per sheet. My batter was a little runny, but the cookies still baked up into nice circles.

Bake 12 to 15 minutes or until edges are light golden brown. Cool 5 minutes; remove from cookie sheets. Cool completely.

Make some of the white icing first. You can do it all at once, but given how sensitive white chips can be to heat, I recommend making a small batch first. Combine a tablespoon of the heavy cream with ⅓ cup of the white chips. Microwave at 50% power for 30 seconds. Stir until smooth. If chips do not completely melt in 30 seconds, continue microwaving for 20 seconds and stirring until mixture is smooth. Spoon white mixture over as many cookies as you can, then repeat procedure with remaining white chips and cream.

Repeat with dark chips. Combine 1 tablespoon of the heavy cream and ⅓ cup of the dark chips. Microwave at 50% power for 30 seconds, then stir well. Repeat until chocolate is melted and smooth. Spoon ganache over other side of cookies.