Should you par-bake your mushrooms before stuffing?

No. When mushrooms cook, they expel a lot of moisture. If you're stuffing them, the moisture will make the stuffing soggy and ruin the texture.

Instead, cook your mushrooms stove top. Heat some oil or butter in a skillet over medium heat. Once the oil is hot, add your mushrooms and cook until they're softened and lightly browned. Then remove them from the skillet and let them cool before stuffing.