Brown chopped onions in butter until translucent. Sprinkle flour, wet with vegetable broth and white wine. Season. Cover and let gently simmer for 20 minutes.
Place egg within shell in boiling vinegared water for 10 seconds and remove. Using a spoon, give a slight circular motion to boiling water and crack egg in the middle of the swirl. Count a good three minutes. Collect egg with a skimmer and set aside on a plate.
Pour some soup into a bowl. Sprinkle with grated cheese. Pour soup again and cover with a slice of toast and more grated cheese. Grill for 10 minutes.
