Hazırlanışı
1Preheat oven to 190°C. Butter a 2-liter gratin dish.
2Melt 41g butter in a saucepan, add sliced onion, sweat gently 3–4 minutes until translucent without browning.
3Sprinkle 24g flour over onion, stir constantly 1–2 minutes to form a roux.
