Alaska Gratin

• 1/2 salmon mixture over
• 280 gr old potatoes
• 130 gr pink alaska salmon (canned)
• 90 ml milk
• 55 gr courgettes
• 50 gr cheddar cheese
• 45 ml greek yogurt
• 36 gr button mushrooms
• 14 gr butter
• 8 gr chives (freshly chopped)