To prepare cake, preheat over to 350F. Grease and line an 8-inch square cake pan.
In a large bowl, sift flour, baking powder, baking soda and salt. Mix well.
With the mixer on low, slowly add half the flour mixture; mix until just blended. Add the buttermilk, mix until just blended. Slowly add remaining flour mixture, scraping down sides of the bowl with a spatula, as necessary, until just blended.
Pour batter into the prepared pan. Transfer pan to oven and bake for 18 to 20 minutes. 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 your mixer on low, beat until the sugar incorporates with the butter. Add vanilla and heavy cream, 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. Shape the balls into cone shape, 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 pop. 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 desired patterns to decorate the Christmas trees.