Start by heating the olive oil and butter in a wide pan over medium heat. Add the chopped onion and cook gently until soft and translucent, not browned. Stir in the garlic and let it cook for about 30 seconds until fragrant.
Add the arborio rice to the pan and stir well so each grain is coated in the oil and butter. Let it toast for about a minute, which helps build flavor and keeps the rice from turning mushy later.
Stir in the grated or finely chopped beetroot. The rice will immediately start turning pink, and the earthy aroma will come through. Mix well so the beetroot is evenly distributed.
Begin adding warm stock one ladle at a time, stirring gently and often. Let the rice absorb most of the liquid before adding more. This slow process is what creates the creamy consistency.
Continue adding stock and stirring for about 20 minutes. The rice should be tender but still have a slight bite in the center. If you run out of stock, you can add a little warm water.
Once the rice is cooked, remove the pan from heat. Stir in the parmesan cheese, a squeeze of lemon juice, and season with salt and black pepper. Cover and let it rest for two minutes before serving.