How to make
The pork sirloin is cleaned from the fat and veins, if any. It is dried with kitchen paper on all sides.
Heat the fat and place the meat to seal on all sides for 2 minutes. There should be no raw meat left.
Remove it and place it in a baking pan and leave the pan aside, because we will need it again, but later.
In a bowl, mix the mustard, ketchup, yogurt, pomegranate sauce / pomegranate molasses, freshly ground black pepper, cumin and salt. Spread this mixture on all sides of the meat in a thin layer. Pour the liquids into the baking pan, so that they do not wash away the spices.
Clean the garlic heads and cut the end, because then the roasted garlic cloves come out more easily. Add it to the baking pan.
According to Jamie Oliver's idea, wet the baking paper under running water. Crush it in a handful, squeeze it and cover the meat so that the edges of the paper remain inside, they should not come out of the baking pan. Cover tightly with two sheets of aluminum foil on top, pressing the edges to the edges of the baking pan so that steam does not escape during baking.
Place it in an oven at 430°F (220°C) and after boiling reduce the temperature to 280°F (140°C). Cook for about 3.5 - 4 hours. This method of slow cooking is close to a slow cooker.
After this time has passed, remove the baking pan from the oven, unwrap it and transfer the roasted meat into a suitable container. Cover tightly with aluminum foil. When transferring, do not prick with a fork, but use a spatula.
Return the baking pan onto the heat again. Put the mushrooms with 2 tbsp. of water to stew, salt them. They should remain completely in the fat. Then pour 1 cup of broth or hot water and let it reduce to 1/3 of the liquid.
Squeeze 2-3 of the roasted garlic cloves into the roasted pork sauce and mash them well. Strain through a large sieve, rubbing with a spoon to make it finer. Add to the mushrooms, wait for it to boil again and thicken with 1 tsp. of starch, diluted in a little cold water. Turn off the heat.
Add the piece of butter to the mushroom sauce and stir until it melts. Pour the sauce over the pieces of meat and cover for 10 min. with a lid before cutting.
Garnish
Peel the potatoes and cut them into equal sized cubes. Cover with enough salted water and leave them on the stove until they are cooked. Strain and mash with a potato press.
Add the hot milk and cubed butter. Continue mashing with the press until you have fine mashed potatoes, about 15-20 minutes.
The Pork Sirloin with Mushroom Sauce is ready.
