Courgette Casserole

• 2 pounds courgettes, sliced
• salt
• 1 Spanish onion, finely chopped
• butter

Simmer courgettes in a little salted water in a covered saucepan until tender but still crisp - about 5 minutes. Drain; whisk in electric blender. Sauté onion in butter until transparent; add to courgette mixture with eggs, sour cream and 3