Clean and trim the mushrooms. Cut in half depending on size. Peel and chop 2 onions. Wash and halve the tomatoes. Heat the oil in a large pan. Fry the minced meat in it until crumbly. Add onions and mushrooms and fry for 3-4 minutes.
Add tomatoes, tomato paste and mustard. Sweat briefly while stirring. Remove from heat and season with salt, pepper and sugar. Leave to cool slightly.
Let the dough sheets rest at room temperature for about 10 minutes. Wash herbs, dab dry. Finely chop parsley and dill. Cut chives into small rolls. Grease a springform pan (26 cm Ø).
Melt the butter. Whisk the eggs, mix with 100 g cheese and about half of the parsley into the minced meat mixture. Remove the dough sheets from the packaging and spread them out on a slightly moistened kitchen towel.
Line the mould overlapping with the pastry sheets, brushing each sheet with butter.
Sprinkle the dough base with breadcrumbs. Spread the chopped mass on top. Cut off the protruding edge of the dough with scissors. Use dough remains for other purposes. Spread the edge of the dough with the remaining butter. Sprinkle 50 g of cheese on the minced meat mixture.
Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 30-35 minutes.
Drain the cucumbers and collect the stock. Peel 2 onions, dice cucumber and onions finely. Wash apple, grate dry, quarter and core. Dice the apple as well. Mix gherkins, onions and apple with remaining parsley and dill.
Stir in 1-2 tablespoons of the collected brew. Mix sour cream with chives, season to taste with salt and pepper. Serve salsa and sour cream with the minced meat pie.