Preheat the oven to 180 C.
Wrap the beets and 3 cloves of garlic in foil and roast for 45-50 mins. You know the beets are cooked when a knife inserted into them goes through without any resistance.
Cook pasta according to packet instructions. Drain and add to a pot.
Roughly quarter the beets and add to a blender jar. Squeeze out the roasted garlic and add to the jar. Add the cashews, raw garlic clove, milk, red wine vinegar, and salt. Blend it all together to a smooth purée.
Add the beet sauce to the cooked pasta and toss to coat. Season with more salt and freshly cracked black pepper. (The nubbly texture of cracked pepper is a nice contrast against the sweetness of the beets here. If you don’t own a pepper mill, coarsely pound in a pestle and mortar/use a blender.) Taste and adjust seasoning.
Serve with lots of crumbled feta over the top. Best served warm or at room temperature.
Keeps refrigerated (without the feta) for up to 3 days or in the freezer for up to a month.