Preheat oven to 350ºF. In a large sautè pan heat the olive oil over medium-high heat and cook the sausage. Once fat has rendered and the meat has crisped, remove with a slotted spoon to a large bowl. Add the bread to the bowl and toss.
Drain the fat but do not wipe clean. Add butter to the pan, and once melted, add the carrot, celery onion, and mushrooms. Season with salt and sautè; until softened, about 5 minutes. Transfer to the bowl with the sausage and bread.
Add the chicken stock, milk, eggs, parsley, Hidden Valley The Original Ranch Salad Dressing & Seasoning Mix, and a large pinch of salt and pepper. Toss everything to combine.
Lightly spray the muffin tins with nonstick cooking spray. Spoon half of the mixture into the muffin tins and then press to compress the mixture into the tins. Top with the remaining mixture. Cover lightly with aluminum foil.
Bake for 10 minutes, covered, and then remove the aluminum foil. Cook an additional 5 to 10 minutes, until lightly browned and crisped on top. Cool slightly before serving.
For safe meat preparation, reference the USDA website.