
Preheat oven to 350F (180C). Line 9x13 inch (22x33 cm) baking dish with parchment paper and lightly grease with olive oil.
Combine in the bowl of a food processor, peeled beets and lentils. Process until smooth, scraping down sides of the bowl once or twice. You should be left with about 2 cups (500 ml) of beet and lentil puree.
Sift together flour, cocoa, baking soda, and salt in a large mixing bowl.
Beat eggs in the bowl of a stand mixer until frothy, about 1 minute. Beat in olive oil and maple syrup until glossy, another 2 minutes.
Beat in coffee, vanilla, and beet/lentil puree until incorporated, scraping down the sides of the bowl.
Add the dry ingredients on low speed until incorporated. Pour in buttermilk and chopped chocolate. Gently mix.
Scrape into prepared baking dish. Bake for 35-45 minutes until wooden toothpick comes out clean. Cool on baking rack. Then cut into squares.