Preheat oven to 375 degrees. Line baking pan with parchment paper. In a large mixing bowl, place lean ground beef and the next 8 ingredients. Add salt and pepper, then combine, mixing llightly. Shape into a 2 inch thick rectangular shape on baking pan. Cover meatloaf with bacon slices. Bake at 375 degrees for up to 1 1/2 hours - checking after 1 hour, then fifteen minutes until bacon is done. Remove from oven to rest, scraping up meat juices from baking sheet. When meatloaf has cooled, Frost with mashed potatoes and top with finely grated sharp cheddar cheese. Run back in 375 degree oven until potatoes are heated through and cheese has melted. (Potatoes May spread, when done - simply allow to cool a bit and smooth into a pleasing shape. Decorate with reserved and sliced mushrooms - and either parsley or fresh sage leaves if available. When meatloaf has cooled down, with a long spatula you may remove to a serving platter with a long meat spatula or...decorate the rest of the baking sheet with garnishes.