Preheat oven to 400°F (200°C).

Line a baking sheet with parchment paper.

Heat olive oil in a saute pan over medium-high heat.

Add Italian sausage and chopped shallots to the pan.

Saute until sausage is browned and cooked through, breaking it up with a spoon (5-7 minutes).

Remove the sausage mixture from the pan.

Place the sausage and mushroom stems in a food processor.

Pulse until finely chopped and combined.

Add pine nuts to the food processor.

Pulse a few times until slightly smooth.

Transfer the mixture to a mixing bowl.

Fold in grated Swiss cheese, Gruyere cheese, and heavy cream.

In a separate bowl, combine breadcrumbs and chopped fresh parsley.

Place the mushroom caps, hollow-side up, on the prepared baking sheet.

Spoon the sausage and mushroom mixture into each mushroom cap.

Top each mushroom with the breadcrumb mixture.

Bake until golden brown, about 20 minutes.