Preheat the oven to 400 F/ 200 C/ gas mark 6. Peel the beetroot, cut into wedges and place on top of a baking sheet. Add the onion and garlic, season and drizzle with 2 tablespoons of oil. Bake for 30 minutes or until the beetroot is tender. Halfway through remove the garlic from the oven and stir the beets and onion. Whilst the vegetables are in the oven boil the pasta in salted water according to packet instructions. Drain and reserve at least ½ cup of the water from cooking.
Remove the vegetables from the oven, puree along with the garlic, yogurt and ⅓ cup of the water from cooking the pasta (you can add more later if needed). Season to taste and set aside.
Combine the beetroot sauce with the pasta and grated parmesan, stir, adjust the seasoning (and add more water if needed) and serve.
Half way through roasting the vegetables remove the garlic from the oven (it doesn't need to roast as long as the beetroot).
The sauce: Add the water gradually to get the consistency you want.
You may have to reheat the sauce before combining with the pasta.
The pasta: Use any pasta shapes you like.
Best served immediately. Leftovers can be refrigerated for up to 3 days. You may have to add a splash of water (and adjust the seasoning) when reheating the pasta.
Serve with arugula (rocket leaves), a drizzle of oil, crispy salad, caesar salad, garden peas, green beans or steamed broccoli.
Freezing: I recommend only freezing the sauce and cooking the pasta just before serving. The process of freezing, defrosting and reheating might make the pasta soggy so it's best to boil and combine it with the beet sauce when you are ready to serve this dish.