Preheat oven to 400°F.

Butter a 9 x 13-inch baking dish with 2 tablespoons of butter.

Place the bacon in a large deep skillet. Place over medium high heat. Fry until evenly brown. Remove to a paper towel-covered plate to drain and allow to cool to the touch. Crumble. Set aside.

Place frozen spinach in a medium saucepan. Add 1/4 cup water. Place over medium heat and bring water to a boil. Lower heat to medium Cook, covered for 10 minutes. Uncover and stir. Remove from heat and drain. Set aside.

Remove stems from mushrooms. Finely chop the stems.

Arrange mushroom caps, "cup side" up, in the baking dish.

Melt 3 tablespoons of butter in a medium saucepan over medium heat.

Add onion and garlic. Stir and cook 5 minutes, or until tender.

Add bacon, spinach, chopped mushroom stems and heavy cream. Stirring, bring the cream to a boil.

Remove from heat and mix in the Parmesan cheese, salt and pepper, to taste.

Using a small spoon, stuff each mushroom cap with a generous dollop of the mixture.

Drizzle with 2 tablespoons of melted butter.

Place dish in preheated oven. Bake for 30 minutes until lightly browned.

Remove and place on a serving dish. Serve immediately, hot.