Peel the garlic and press it through a garlic press. Wash the marjoram, dab dry and chop. Mix butter, garlic, marjoram and lemon juice with a fork. Season with salt and pepper.
Clean and peel the beetroot (Attention! Stains strongly - it is best to put on disposable gloves) Cut the beetroot into slices about 1 cm thick.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3). Place beetroot in 4 portions on large pieces of aluminium foil, spreading the butter mixture in flakes between them. Seal to packages.
Bake in a hot oven for about 45 minutes.
Meanwhile, mash the cheese with a fork and mix with crème fraîche and milk to a smooth sauce. Season with salt and pepper.
Peel onions and cut them into thin rings. Turn in flour and fry in hot oil until crispy. Take out and let drain on kitchen paper.
Remove the beetroot from the foil and put it on plates with the liquid butter. Serve with blue cheese dip and onions. It goes well with farmhouse bread.