For Lasagna Sauce: Heat the olive oil in a large lidded pot. Put the chopped onion in and fry until the onion turns translucent. Add the smoked paprika. Add the ground pork and beef and fry until browned. Season with salt and pepper. Add the chopped tomatoes and the tomato puree and bring to a boil. Reduce the heat to the lowest setting and let simmer for a couple of hours, until the sauce is thick. Set aside. For White Sauce: In a separate pan, melt the butter and add the flour and make a roux. Cook this for a few minutes but do not allow it to color. Add the milk to the roux a little at a time and allow it to absorb the first few times before putting more in. Add the remaining milk and cook until the consistency of heavy or double cream. Grate in about nutmeg and set aside. To Assemble: Put in a thin layer of the meat sauce into a lasagna dish and put in a layer of lasagna sheets. Alternate the layers until you get up to about a half inch below the rim of the dish, ending with a layer of lasagna. Pour on the white sauce. Put into a preheated 375 degrees F oven for 25 to 30 minutes until the white sauce turns golden brown.