Heat the oven to 350. Wrap the beets individually in aluminum foil. Place the beets on a rimmed baking sheet and roast until very tender, 1 to 1 hour 20 minutes. Remove and let cool until just warm to the touch in the foil. Peel the beets and coarsely chop.
Place the chopped beets in the large bowl of a large food processor fitted with the blade attachment. Process until chunky, stopping to scrape down the sides of the bowl with a rubber spatula. With the food processor running, add the oil and continue processing until very smooth. Add buttermilk and eggs. Puree until smooth.
Add the flour, sugar, cocoa, baking powder, baking soda, and salt. Pulse until well-combined. If you have a large food processor you can continue in the processor, if not, sift the dry ingredients in a large bowl and add the wet ingredients from the food processor to the dry and stir until combined by hand.
For cupcakes: Line the tin with cupcake liners. Using a ice cream scoop, a spoon, or a liquid measuring cup, fill the liners no more than 2/3 full. Transfer to the oven and bake until firm, about 10 minutes. Remove to a rack to cool.
Meanwhile, to prepare the frosting, in the bowl of a mixer fitted with the paddle or beater attachment or with a handheld mixer, cream the cream cheese and butter on medium speed until very smooth. Sift over the confectioners’ sugar. Beat until light and fluffy. Beat in the vanilla. If too stiff, add the milk, 1 teaspoon at a time, to achieve the correct consistency. Add black food coloring and stir until pale grey.
Using an offset spatula, ice the cupcakes with the grey icing. Once the icing is slightly set, use a straw to make “plates” across the top of the cupcake.
To make the tails: Working with 1 at time, place a tootsie roll in a glass bowl and microwave until warm and barely soft, about 5 seconds, depending on the strength of the microwave. Roll the warm tootsie roll into a long-pointed tail. While warm, use a toothpick to notch and create the tail plates.
Think of Steel Magnolias and serve within 2-3 days.