Peel and cut the potatoes, clean the broccoli, mince the onion and garlic.
Put the potatoes in about 4 cups of boiling water and cook for 20 min. Add broccoli, onion and garlic and let cook another 20 min.
After cooking, drain the vegetables and puree with a potato masher.
Add 2 oz of butter (you can also use less), cut into small pieces. Add salt, pepper and nutmeg.
Mix the sour cream, 2 egg yolks and 4 oz of grated cheese. Stir this mixture into the pureed vegetables.
Preheat oven to 400° F.
Finally, butter a baking dish (buttering is optional), fill with the seasoned puree. Cover with the remaining grated cheese.
Allow to brown in the oven about 15 minutes.