Roast the washed beets with the skin on in a 350°F/180°C oven until beets are tender for about 1 hr. for medium beets. Add extra time for larger beets. Remove from over and gentle remove outter skin when cooled. Pureed roasted beets in a food processor or blender until completely smooth.
Sift together the flour, baking powder, salt, and cinnamon. Set aside.
In a large bowl, stir together the beet puree, granulated sugar, eggs, oil, and vanilla. Using a rubber spatula, stir in one-third of the flour mixture, continuing to stir just until the flour disappears. Do not beat or over mix. Repeat, adding the remaining flour mixture.
Cream the butter with a hand mixer until creamy and smooth. Add the confectioners' sugar, cream, orange oil, and vanilla and beat on low speed until incorporated, about 2 minutes. Add the orange juice, a little at a time, until the buttercream is fluffy and smooth.
Spread a thick layer of buttercream on the top of each cooled cupcake. The cupcakes can be store at room temperature for up to 2 days or freeze for up to 1 month.
Pure orange oil is an essential oil that is cold pressed from the rind of oranges. Do not confuse it with pure orange extract, which is alcohol flavored with orange oil. Look for pure orange oil in the baking section of natural foods stores. Two brands available are Boyajian and Frontier.
Recipe adopted via 'Roots' by Diane Morgan