For the cream of onion soup, halve the onions, cut into strips and sauté in a pot in hot butter until light. (The onions should not take on color.) Then dust with flour and stir briefly.
Deglaze with vermouth and white wine and boil down. Pour in the chicken stock and simmer on low heat for about 5-7 minutes. Pour in whipped cream and simmer for another 3 minutes.
In the meantime, for the croutons, remove the crusts from the toast and cut into cubes. Melt butter in a pan and fry the bread cubes until golden brown. Remove from pan and drain on paper towels. Season lightly with salt.
Coarsely chop the dill. Season the soup with salt and pepper, blend with a hand blender and strain through a sieve.
Before serving, bring the cream of onion soup to the boil again briefly. Add the whipped cream and blend. Pour into deep plates and garnish with croutons and dill.