Place the sausage in a large skillet set over medium heat. Brown and crumble the sausage. Transfer the sausage to a paper towel-lined plate and remove all but 2 tablespoons of rendered fat from the skillet.
¼ pound hot pork sausage
Reduce the heat to medium-low and add the onions and sauté until the onion is translucent. Add the garlic and cook for an additional 15 seconds, stirring continuously.
½ cup minced onion, 3 cloves garlic
Pour in the wine to deglaze the pan and allow the liquid to evaporate.
¼ cup dry white wine
Add the minced mushroom stems and cook for 2 minutes, stirring continuously. Salt and pepper to taste.
Reserved minced mushroom stems
Transfer the onion/mushroom mixture to the sausage to cool.
In a medium bowl, whisk together the cream cheese, goat cheese, herbs de Provence, and egg yolk.
3 ounces cream cheese, 3 ounces goat cheese, ½ teaspoon herbs de Provence, 1 egg yolk
Add the Parmesan cheese and whisk until incorporated.
3 tablespoons freshly grated Parmesan cheese
Add cooled sausage/onion/mushroom mixture, stir well, and refrigerate 15 minutes to firm a little.