Brown and crumble sausage. Set aside to cool.
Add onions and garlic to the same skillet; cook for 2 minutes over medium low heat.
Add in chopped garlic and sauté for 1 minute.
Stir in spinach a handful at a time and sauté until wilted.
Add salt, pepper and nutmeg, stir to combine.
Stir in heavy cream, then cream cheese.
Break up cream cheese with a wooden spoon and stir until thoroughly combined.
Set mixture aside to cool.
When mixture is lukewarm, stir in parmesan cheese; set aside
Gently remove stems from mushrooms; set aside.
Lightly oil a baking dish and place mushroom caps inside, to fit snuggly.
Using a small cookie scoop, fill the caps with a generous amount of sausage filling.
Bake at 400• for 20 to 25 minutes, or until golden brown. Allow to cool at least 5 minutes before serving.