Source: Farmer John’s Cookbook: The Real Dirt on Vegetables by John Peterson and Angelic Organics
Scrub the beets with a vegetable brush and trim roots. Trim stems and save greens for some other use. Bring a pot of water to a boil and add the beets. Boil for 20-30 minutes, or until the beets are tender and the skins slip off easily. Let the beets cool a little, the slip the skins off under cold water and then puréethe beets in a blender or food processor. You should have about 2 cups of beet purée.
Preheat your oven to 375F. Butter and flour a Bundt pan and set it aside.
Fill a medium saucepan about halfway with water and bring the water to a boil. Reduce to a simmer and set a heat-proof bowl over the simmering water. Place the chocolate and ¼ c. of the oil in the bowl and heat, stirring frequently, just until the chocolate melts.
Combine the eggs and sugar in a large bowl and beat with an electric mixer until fluffy. Slowly beat in the remaining oil, the chocolate mixture, beets, and vanilla.
In a medium bowl, whisk together the flours, baking soda, and salt. Gently stir the flour mixture into the egg and chocolate mixture until just combined.
Pour the batter into the prepared pan and bake until a toothpick inserted near the center comes out clean, about 45 minutes. Remove the pan from the oven and cool on a wire rack for 30 minutes. Carefully remove the cake from the pan and allow it to cool completely before sprinkling with powdered sugar to serve.