Peel, wash and slice the potatoes. Precook in salted water for about 10 minutes
Leek clean, wash, lengthwise halve and cut into pieces. Add to the potatoes about 2 minutes before the end of the cooking time and cook. Then drain everything well
Wash apples, remove seeds (e.g. with a cookie cutter) and cut into slices. Sprinkle with lemon juice. Halve the bacon. Mix sour cream, milk and egg. Season with salt, pepper and thyme. Coarsely grate Gouda
Fill potatoes, leek, apples and bacon into a greased casserole dish. Pour egg sour cream over it, sprinkle with Gouda. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C / gas mark 3) for 30-40 minutes until golden brown. Garnish with pink berries as desired