Before getting started, chill the brie (we’ll freeze it for 20 minutes or so), and use a sharp knife to trim the rind off the top and sides of the brie.

Cover in plastic, chill until use.

Beat butter and cream cheese until well mixed and soft. Slowly add flour.

Once all flour is added, turn out and knead just until well incorporated and smooth.

Form a disk or ball, wrap tightly in plastic wrap, and refrigerate for about 30 mins.

As the dough chills, make your filling.

In a large nonstick pan, saute mushrooms, onion, and garlic cloves in the olive oil. Cook until onion is translucent and mushrooms a soft.

Once all the liquid that releases from the veggies cooks off, add balsamic vinegar and continue to cook for two minutes.

Remove from heat, season with salt and pepper, to taste.

Preheat oven to 400 F.

Roll chilled dough out to about ¼″ thick.

Place trimmed brie in the center of the dough, top with mushroom mixture.

Loosely fold in the ends of the dough to the center, overlapping for a loose seal.

Whisk the egg and balsamic vinegar together in a mug, brush all over exposed surface of the dough.

Bake for 20-25 minutes, until desired level of golden.