Sift the flour, add the milk, slightly heated, to it, and the remaining products. Knead a add, while adding a little more flour onto the counter, to obtain a smooth dough. Cut it into 4. Form a ball from each. Cover with a towel and leave it as is, while you make the stuffing.
For it, heat 3-4 tbsp oil in a deep pan, and put the peeled and finely chopped mushrooms in it. Then add the chopped onions.
Debone the chicken legs, dice it, dice the ham. Add them to the mushrooms and braise 3-4 min. Season with the spices, stir and remove from the heat.
Peel the tomato, dice it and add it. Stir and let cool.
Next, dice the emmental and add it as well.
Roll out each ball onto the counter, sprinkled with flour itself, so it doesn't stick to the rolling pin. Roll each ball out into a thin sheet, to a square about 11 3/4″ (30 cm). Spread it out onto a sheet of paper or cloth. Do this for all of them.
Lay out a tray with baking paper. Lay out 1 sheet onto the tray at one end of it. Put some of the stuffing in the middle but make sure you distribute them out so you have equal amounts for all 4. Gather up the remaining dough in your hand, wrap it up like a sack, then twist once, drop the dough from a decent height to slap down.
Work fast, so it doesn't stick and does not rip. Stretch the ends out toward the middle and then fold underneath to shape the bohcha itself. Repeat this with the other sheets. Place in the other end of the tray.
Smear them with beaten egg yolk, mix with a spoon of milk. Bake in a preheated 446°F (230 °C) oven for 15 min.
Bake in the middle of the oven with the fan on. Bake with the oven turned off, for 5 min.