Preheat oven to 350 degree. While oven is preheating, wash mushrooms, remove stems. Dice stems very finely; set aside.
In a small skillet, heat about a tbsp of bacon grease over med heat; add the minced stems and onion. Saute for about 2 minutes, mushroom stems and onions are soft. Add the minced garlic, continue cooking for another minute or until fragrant from the garlic. Add a bit more bacon grease if necessary.
In a medium bowl; mix cracker crumbs, diced mushroom stem mixture, bacon, 1/2 cup of the shredded cheddar and spoon about a tablespoon into each mushroom cap.
Sprinkle with remaining 1/4 cup shredded cheddar cheese. Drizzle mushrooms with 2 Tbsp. melted butter.
Bake uncovered in a 350 degree oven for about 15 minutes.