Champagne Pea Soup (Crème Ninon)

200 g frozen peas
1 finely chopped onion
1 tbsp butter
6 dl vegetable broth
1 dl cream
1–2 dl champagne / sparkling wine
salt and black pepper from a mill to taste

Sauté the chopped onion in butter in a saucepan. Add the peas and vegetable broth. Boil for half an hour and purée with an immersion blender. Season with salt and black pepper. Add the cream and sparkling wine before serving.