Brown the sausage. Heat a large Dutch oven over medium-high heat. Add the hot sausage and begin breaking it into small pieces with a wooden spoon.
Add the ground beef. Add the lean ground beef to the Dutch oven. Cook both meats together, stirring and breaking them into crumbles with a wooden spoon or potato masher, until evenly browned.
Cook the onion and celery. Increase the heat to high. Add the finely chopped onion and celery to the browned meat. Stir and cook for approximately 1 minute, until the onion begins to soften.
Add the carrots. Stir in the sliced carrots and continue cooking for another 2 minutes.
Add the seasonings. Add the garlic, onion soup mix, kosher salt, and black pepper. Stir continuously for approximately 2 minutes, until the garlic and seasonings become fragrant.
Pour in the liquids. Add the beef broth, crushed or diced tomatoes, water, and bay leaf. Stir thoroughly and bring the mixture to a boil, stirring occasionally.
Add potatoes and green beans. Stir the frozen hash brown potatoes and frozen cut green beans into the boiling stew. Continue heating until the mixture returns to a boil.
Simmer until tender. Reduce the heat slightly, cover the Dutch oven, and simmer until the potatoes, carrots, and other vegetables are tender.
Prepare the mushroom skulls. Meanwhile, clean the whole button mushrooms and cut each one vertically in half. Place each mushroom half flat-side down on a cutting board.
Create the skull faces. Use a clean straw to make two small holes in each mushroom half for the eyes. Make a third small hole for the nose, or carefully use a paring knife to create two small slits.
Add the mushroom skulls. Gently place the decorated mushroom halves into the simmering stew. Cook for approximately 10 minutes longer, or until the mushrooms are just tender.
Adjust the seasoning. Remove the bay leaf. Taste the stew and add more salt or black pepper if desired.
Garnish and serve. Ladle the warm stew into bowls, arranging a few mushroom skulls on top of each serving. Sprinkle with freshly chopped parsley and serve.