What's the secret?  Chef Missy fills us in

If using raw spinach, thoroughly wash it, even if the package says “prewashed.” Bring spinach or collards and water to boil in a medium pot. Turn heat to low and allow to simmer for 10 minutes.

If using frozen blueberries, quickly rinse them under cold water to thaw a little, and then drain.

Fill the bowl of your food processor with the blueberries and cooked spinach, (or collards) along with the lemon juice and 2 tablespoons of water, and puree on high until as smooth as possible. Stop occasionally to push top contents to bottom. If necessary, add the rest of the water to make a fairly smooth puree.

This amount of spinach and blueberries makes only about 1 cup of puree. Double the recipe if you want to store another cup of the puree. It will store in the refrigerator up to 2 days, or you can freeze 1/4 cup portions in sealed plastic bags or small plastic containers.

Combine this purple egg mixture with the cooled chocolate mixture.