You can also use 1/2 sausage and 1/2 hamburger. I have also used lump crab meat. And, I have also stuffed jalapenos with the same stuffing (wrapped in bacon). I have never measured the seasoning so it is all to your own taste.
Brown the sausage. Drain and save the grease. Add grease with 2 T. Butter and saute the onion, celery, and minced stems. Add back the sausage.
Put cream cheese, shredded ceese and seasonings to a bowl and mix well. Add breadcrumbs and parmesan. Mix rest of butter (melted) to meat mixture, and fold the two mixtures together.
Add more breadcrumbs or parmesan if mixture is too loose. Spoon into the mushroom caps. I use a cookies scoop. Sprinkle with more cheese of your choice. Bake at 350 degrees for 20-30 minutes until bubbly.