Preheat your oven to 400 degrees F. Grease a glass or ceramic baking dish (a square 8-inch baking dish should work).
Wash and dry the mushrooms. Use a paring knife to gently remove the stems, as shown in the video below. You’ll be left with about 6 oz of mushrooms after removing the stems.
In a medium bowl, use a rubber spatula to thoroughly mix the cream cheese with the salt and the spices. Mix in the gruyere.
Spoon the mixture into the mushroom caps. Pack about a teaspoon into the cavity, then add a small mound on top of the mushroom. You can use your hands to pack the mound in and shape it so that it’s smooth. You might be left with a bit of unused cheese mixture. If you had additional mushrooms in the package, you can stuff them too.
Place the mushrooms in the prepared baking dish. Bake until the cheese has melted and the mushrooms are tender, 10-15 minutes.
Place the stuffed mushrooms on paper towels to absorb extra liquids. Let them cool for 5 minutes before serving.
It’s best to use large mushrooms in this recipe and make them about the same size. I often buy two containers of mushrooms, so that I can pick the best ones for this recipe.