I make this so often when I get a lot of beetroots from my vege delivery box. It's liberally adapted from this recipe. I double it for efficiency and because a double recipe fits perfectly in my large baking dish. The original recipe includes a chocolate ganache which I don't usually make.

Notes

Servings: 24
Prep Time: 20 minutes 
Cook Time: 35-50 minutes depending on pan size etc.

Ingredients

• 1.5 cups (230 g) plain flour (can use gluten-free)
• 1 cup (80 g) cocoa powder
• 2 teaspoons baking soda
• a pinch of salt
• 1 cup (250 mL) rice bran oil (or other neutral oil)
• 1 cup (200 g) sugar (I prefer brown, YMMV)
• 5 large eggs
• 2 teaspoons vanilla extract or a smaller amount of vanilla paste
• 2 tablespoons apple cider vinegar
• 400 g beetroot
• 200 g chocolate chips, buttons, or chopped chocolate (approximately, vary up or down depending on taste; this is quite a lot of chocolate) (here I use the best chocolate in the world, Whittakers 50% dark, but if you're a pleb from overseas... get whatever doesn't use slave labour or palm oil)

Instructions

• Prepare the beetroot. I generally chop into 2 cm cubes and then steam until soft. If I have too many beetroots and not enough time I will freeze the cubes and then steam straight from frozen. This can take up to an hour from frozen - I usually leave it going while I do other chores or work. 
• Preheat the oven to 180ºC (fan 160ºC). Prepare your tins - I line a large brownie pan for this recipe, which I doubled from the original, or two 12-hole muffin trays.
• In a bowl whisk together flour, cocoa powder, sugar, baking soda, and salt. Toss the chocolate chips/chunks through to coat with flour. This helps them not sink to the bottom while cooking, although this recipe can run on the lighter side and suffer from a bit of sinkage.
• To a food processor or blender add the olive oil, eggs, vanilla extract, cider vinegar, and the chopped beetroot (make sure the beetroot has cooled a bit and the eggs are added last to avoid cooking the eggs directly in the blender). Blend until smooth and creamy.
• Add the blended ingredients to the dry ingredients and give a good stir to just combine. Pour into the prepared cake tin/s and bake for 30-50 minutes until an inserted skewer comes out clean. (Alternatively, to make cupcakes spoon the batter into the prepared muffin tray and bake for 20-25 minutes.)
• The original recipe includes a chocolate ganache, which I don't usually make, but may be of interest if you don't use chocolate bits.
• This cake keeps well for several days, covered at room temperature, a bit longer in the fridge, or frozen indefinitely.