Melt your chocolate chips in the microwave in 30-second intervals, stirring after each. Alternatively, you can melt on the stovetop in a double boiler.
Put a dollop of melted chocolate into each muffin liner and spread around with the back of a spoon, ensuring you get about 1/3 of the way up the sides. Put the muffin tray in the fridge for the chocolate to set.
In a stand mixer, combine the butter, heavy cream, powdered sweetener, and vanilla. (This is your egg white mixture.) Put a dollop of egg white into each chocolate cup and make an indent with your finger.
Remove half of the remaining egg white mixture from the bowl and set aside.
Add yellow food coloring to 1/4 cup of the egg white mixture. (This is your egg yolk mixture.) Put egg yolk mixture in the fridge for 10 minutes so it is easier to scoop.
Using a melon baller or small spoon, make 12 small balls with the egg yolk mixture. Roll between your hands to smooth out. Place a yolk in each Cadbury Cream Egg cup.
With the egg white mixture that you set aside, put another dollop on each cup, covering the yolk. Spread out the top layer of egg white with a spoon so you have a flat surface.
Top each Cadbury Cream Egg cup with more melted chocolate.
Return tray to the fridge for another 10 minutes for the chocolate to set.