Bake the beetroot and garlic (~90 minutes)
Peel and cube the beetroot
Roast walnuts, put aside
Fry the onion in butter with the roasted garlic
Add the cubed beetroot and heat through
Cook the pasta alongside
Pour away most of the pasta water and put vegetables in the pan with the pasta
Mix up and put back on a low heat for a few more minutes until the water isn't liquid any more
Take the pot off the heat and crumble in the feta
Stir well until the feta starts to melt and coat the pasta
Plate up and sprinkle with the walnuts, if wanted