Boil the potatoes, preferably with their skins on, until fork tender. Let them cool, then peel and slice into rounds.
Meanwhile, fry the diced bacon in a large skillet or saucepan over medium heat until the fat has rendered and the bacon is lightly browned.
Add the ground meat and cook until browned, breaking it apart with a spoon as it cooks.
Stir in the diced onions and cook until softened and translucent.
Add the garlic, tomato paste, passata, parsley, thyme, chili flakes, salt, and black pepper. Mix well and bring to a gentle simmer.
Cook the meat sauce over medium-low heat for about 45 minutes, stirring occasionally, until rich and thickened.
In a separate bowl, whisk together the sour cream, eggs, and grated cheese until well combined.
Line a baking dish with parchment paper. Arrange a layer of sliced potatoes on the bottom, followed by half of the meat sauce. Add another layer of potatoes, then the remaining meat sauce, and finish with a final layer of potatoes.
Spread the sour cream mixture evenly over the top.
Bake in a preheated oven at 170°C (340°F) for 45 minutes, or until the topping is golden brown and the casserole is bubbling around the edges.
