Preheat oven to 350 degrees F. Place oven rack in middle of oven. Grease a 13-inch by 9-inch baking dish or pan and line with either parchment paper or aluminum foil.
In a large frying pan or skillet over medium-high heat, heat the olive oil and butter. Add onion and cook until softened, approximately 4 minutes. Add garlic and mushrooms; cook until the mushrooms are soft and the liquid has evaporated, approximately 6 to 8 minutes. Season to taste with salt and pepper; set aside to cool slightly before proceeding.
In a large bowl, gently combine eggs, bread crumbs, Parmesan cheese, parsley, thyme, and cooled mushroom mixture. Crumble beef and sausage over the top and mix well. NOTE: I find that using my hands is the best way to mix all the ingredients together.
Gently pat the meat mixture onto a 10-inch by 13-inch rectangle on a sheet of wax paper or plastic wrap. With the longer end facing you, layer the Filling Ingredients on the bottom 2/3's of the meat. First layer the prosciutto, then Havarti cheese slices, basil leaves, and then sun-dried tomatoes.
Grab the edge of the wax paper or plastic wrap closest to you and roll up, jelly-roll style, starting with the long side and peeling the wax paper away while rolling. Once meat loaf is rolled up, seal ends and press down slightly to seal lengthwise seam. Carefully place the rolled meat loaf, seam side down, on the prepared baking dish.
Rolled up beef roll and ready to cook. NOTE: Meat loaf can be refrigerated at this point and cooked later. Bring to room temperature before baking.
Bake, uncovered for approximately 50 to 55 minutes or until the center of the meat loaf registers 160 degrees F. on a meat thermometer (do not overcook or it will be dry). Remove from oven and let the meatloaf rest for 5 minutes before serving.
To serve, carefully transfer the meat loaf to a serving platter using two large spatulas. NOTE: I found it easier to use the aluminum foil to remove from the baking dish to the cutting board. Cut into eight (8) servings.
* Learn How To Make Homemade Bread Crumbs
Prosciutto Stuffed Meatloaf Recipe: https://whatscookingamerica.net/lindasandberg/entrees/prosciuttomeatloaf.htm