Chocolate Beet Cake with Cinnamon-Cream Cheese Frosting

1. For the cake: Preheat the oven to 400 degrees F. Set each beet on a square of foil and drizzle lightly with vegetable oil. Seal the edges to wrap each beet and roast until tender when pierced with a knife, 40 to 45 minutes. Carefully unwrap and let rest until cool enough to handle.
2. Peel the beets while they are still warm and cut into chunks. Add to a food processor and puree until smooth. Let cool completely. You should have 1 cup beet puree. (Save any extra puree for another use.) 
3. Lower the oven temperature to 350 degrees F. Butter and flour two 8-inch cake pans and line the bottoms with parchment.  
4. Sift together the flour, cocoa, baking powder, baking soda and salt in a large bowl.  
5. Whisk together the beet puree, 3/4 cup vegetable oil, sour cream, water and eggs in a large bowl until combined. Whisk in the granulated sugar and brown sugar until smooth. Add the dry ingredients to the wet ingredients and fold to combine. Do not overmix.  
6. Divide the batter evenly between the two prepared pans. Bake until the cake tops spring back when pressed gently and a tester inserted in the center comes out with just a few moist crumbs, 28 to 30 minutes. Transfer the pans to a rack to cool for 15 minutes. Turn the cakes out onto the racks and let cool completely. Remove the parchment.  
7. For the frosting: Beat the cream cheese and butter together with an electric mixer on medium speed until smooth and fluffy, 2 to 3 minutes. Add the confectioners' sugar, cinnamon, vanilla and salt and and beat on low until combined. Increase the speed to medium high and beat until very smooth and light, about 2 minutes.  
8. Transfer one cake layer to a serving plate. Spread about 1 1/2 cups of the frosting over the top of the cake. Top with the remaining cake layer. Spread a thin layer of frosting (about 1 1/2 cups) over the entire cake to create a crumb coat. Refrigerate until the frosting is cold and firm, about 20 minutes.  
9. Transfer about 1 cup frosting to a pastry bag fitted with a star tip. Frost the entire cake with the remaining frosting in the bowl. Pipe rosettes on the top of the cake and garnish with baked beet chips. Chill 30 minutes to set the frosting before serving. Transfer the cake to a serving platter and pipe smaller rosettes of the remaining frosting around the base.

Baked Beet Chips:

1. Preheat oven to 350 degrees F. Line a baking sheet with a silicone baking mat. Trim one end of the beet so it can sit flat on your mandoline (it is not necessary to peel it). Thinly slice the beet about 1/16 inch thick.
2. Separate the slices and put in a medium bowl. Drizzle with the oil and toss well to lightly coat each slice. Sprinkle with the sugar and toss to distribute. 
3. Arrange the slices in a single layer without touching on the prepared baking sheet. Bake, rotating the tray halfway through, until the chips are browned on the edges and crisp almost to the center, 25 to 30 minutes. (It's ok if the very center is still a bit pliable, they will continue to crisp as they cool.) 
4. Let the beet chips cool slightly on the baking sheet, then remove to a cooling rack to completely crisp up.