Preheat oven to 350 degrees F.
Remove the stems from the mushroom caps and reserve the stems for the (Round 2 Bacon Mushroom Quiche).
In a skillet, over medium heat, add the bacon and cook until crisp. Remove from the pan and set aside on a brown paper bag or paper towels to drain.
In the same skillet, add the onions and saute until translucent. Stir in the rosemary, and salt and pepper, to taste, and cook for 2 minutes.
In a small bowl combine the cream cheese with the leftover crumbled corn muffin tops. Stir in the sauteed onion. Finely chop the reserved cooked bacon and stir into cornbread mixture. If the mixture is too dry add a few tablespoons of warm water. Spoon the filling mixture into each mushroom cap. Arrange on a baking sheet and bake until golden brown and crisp on top, about 15 to 20 minutes. Transfer to a serving platter and serve.