To prepare the cake, preheat oven to 350F. Grease and line an 8-inch square cake pan.
In a large bowl, mix together sugar, flour, cocoa powder, baking powder, baking soda and salt.
Crack in the egg, spoon in the sour cream, and pour in the oil and the vanilla. Mix with a wooden spoon until just combined.
Pour in the boiling water, and slowly mix until smooth and liquidy.
Pour batter in the prepared pan, and bake for 20 to 25 minutes. Transfer pan to a wire rack and let cake cool in pan for 15 minutes. Then invert it onto a greased rack. Let cool completely.
To prepare buttercream, beat butter for a few minutes in a standing mixer with the paddle attachment on medium speed. Add powdered sugar and turn the mixer on low, beat until the sugar incorporates with the butter. Add vanilla, heavy cream and cocoa powder, beat on medium speed for another 3 minutes, or until buttercream becomes light and fluffy.
To assemble cake pops, prepare two cookie sheets lined with parchment paper.
Break the cooled cake into a few big trunks by hand, place them into the bowl of an electric mixer fitted with the paddle attachment and mix on medium speed until the big pieces turn into crumbs.
Add frosting gradually into the cake crumbs and blend until the mixture becomes a dough, about 1 to 1 1/2 cups of frosting.
Use a small cookie scoop, roll dough into evenly sized balls and place them on the prepared cookie sheets. Refrigerate for 30 minutes.
Melt small amount of white Candy Melts in the microwave gradually, 10 second intervals and stirring in-between. Dip one end of a lollipop stick in the melted candy and insert into the cake ball. Repeat until you are done. Refrigerate again for 15 minutes.
Remove the cake pops from the refrigerator. Melt all the white Candy Melts in the microwave. Dip each cake pop in the Candy Melts and gently tap off excess. Place cake pop onto a piece of wax paper. Let it dry completely. Repeat with the remaining cake pops.
Place the black Candy Melts in a microwavable Ziploc bag. Microwave on high for 20 to 30 seconds to completely melt the Candy Melts. Push the melted candy toward one corner of the bag. With a pair of scissors, snip off a very small opening, and start piping the skeleton face on each cake pop.