1. Rinse the potatoes, put them in a glass cooking pot with half a cup of water, cover and cook for 5 minutes in the microwave (800 W). Leave to cool, peel and cut into slices of 1 cm thick. Put the leeks in a cooking pot with a cup of water and a pinch of salt, cover and cook for 4 minutes in the microwave (800 W). Drain.
2. Preheat the oven to 180 ° C (item 6). Peel and chop the shallot, fry for 2 minutes in a nonstick skillet with the margarine. Add the leeks and cook for 2 minutes. In a bowl, whisk the egg with Maïzena® and milk. Season with salt and pepper and add a pinch of nutmeg. Stir in half of the gruyere and leeks.
3. Spread a 18 cm diameter pan with oil, spread the slices of potatoes, salt and pepper. Cover with egg mixture. Sprinkle with the rest of Gruyère. Bake for 15 minutes. Let cool. Serve warm or cold.