Heat oven to 400℉/200℃.
Line a small sheet pan with parchment paper. Set aside.
In a small skillet over medium heat, melt butter.
Add mushrooms, garlic, and rosemary.
Sauté until mushrooms are cooked through, about 3-4 minutes.
Add white wine.
Continue cooking for 1-2 minutes, or until mushrooms have absorbed wine. Set aside.
On a lightly floured surface, roll puff pastry to 1/16 inch.
Place brie in center of dough.
Top with mushroom mixture.
Fold dough up and over brie.
Place on prepared pan.
In a small bowl, beat egg and water until smooth.
Use a pastry brush to brush mixture over entire surface of pastry.
Place in freezer for 15 minutes.
Remove from freezer and place in oven.
Bake for 30-35 minutes, until pastry is golden brown.
