First of all, peel the potatoes and cut them into thin slices (preferably with a vegetable cutter). Put on time in a bowl of cold water. Chop the parsley.
Peel the onions and slice thin. In a deep frying pan, heat 4 tablespoons of olive oil, add 1 tablespoon of water and stew the onions, stirring occasionally. Salt the onion and remove the pan from the heat.
In another pan, heat 3 tablespoons of olive oil. Put the peeled and crushed garlic clove, half a tablespoon of paprika and fry for a few seconds. Add minced meat and fry over medium heat for 5-6 minutes. Then remove the garlic, salt, pepper to taste and add the cognac. Fry the minced meat for another 5 minutes and remove from heat.
Heat-resistant baking dish (square or rectangular) grease with butter. Put on the bottom layer of potatoes. Lightly season with salt.
Put a layer of onion on top, then a layer of minced meat. Sprinkle with chopped parsley (some parsley set aside to decorate the finished dish!). Lay out another layer of potatoes, onions and minced meat.
The last layer will be potatoes. Preheat oven to 200 degrees. Tread carefully on the corners of the mold, pour in warm stock (or water).
Cover the gratin with foil and place in a preheated oven for 30 minutes.
After this time, whisk in a bowl (preferably with an electric mixer) Greek yogurt (or sour cream), cream together with a pinch of salt and the remaining paprika.
Remove the gratin from the oven and remove the foil. Put on top of the resulting cream and spread it over the entire surface of the casserole. Sprinkle the grated gruyère cheese on top and place it in the oven for another 20 minutes.
Until Golden brown... Let the finished dish cool down a little, and then serve immediately!