Put the mince in a bowl, add the grated garlic cloves, basil, 1 tbsp sour cream, black pepper and salt to taste. Knead very well and leave it aside.
Heat 2 tbsp oil in a pan, put the chopped into crescents onions in it and braise until softened, leave aside to cool. Separately, peel and finely dice the hard boiled eggs, mix them with the mayonnaise and stir well until homogeneous.
From the mince, form 8 flattened round meatballs in an oiled tray and arrange them with space in between them. On top of each, first put braised onions, then egg/mayo mixture on top.
Grate the potatoes, season them with black pepper and salt to taste and distribute in a pile (like a haystack) on top of the meatballs.
Grate the cheese and distribute it over the potatoes, smear a little of the sour cream on top to obtain a soft cheesy crust.
Put the tray in a preheated 356°F (180 °C) oven and bake about 40-45 min. to a golden crust.