Peel all types of onions, halve them and cut into thin rings. Remove the dark green of spring onions, cut the rest into thin rings and set aside.
Melt butter in a saucepan, add sugar and brown them. Sauté onions and garlic, drizzle with vinegar. Douse with white wine and let simmer. Pour in beef stock and simmer all about 15 minutes. Season with parsley, salt, pepper and vermouth. Add green onion rings.
Toast the toast slices, cover with cheese and pepper. Gratinate in the oven at 180 ° C.