Prepare the Crust: Boil the potatoes until tender, mash them, and press into a greased 23 cm springform pan to form a crust. Pre-bake at 200°C (392°F) for 15 minutes.
Prepare the Filling: Blanch the leeks in boiling water for 3 minutes, then drain and pat dry. Fry the bacon until nearly crispy, then add the onions and cook until soft. Drain any excess fat.
Mix the Egg Mixture: In a bowl, whisk the eggs with crème fraîche, grated cheese, salt, and pepper.
Assemble the Tart: Spread the leek and bacon mixture evenly over the pre-baked potato crust. Pour the egg mixture over the top.
Bake: Bake the tart at 200°C (392°F) for about 20 minutes, or until the filling is set and golden.
Garnish and Serve: Sprinkle with fresh chives and serve warm or cold.
