Caramelized Onion and Balsamic Glazed Mushroom Brie en Croûte

I have a backlog of about half a dozen recipes that I've made in the last week or so and haven't gotten around to writing up yet. I was doing them more-or-less in order. I think I have to jump the queue with this one though. I ended up improvising a bit and I'm afraid that I'll forget what I did if I don't write it down right away.

This recipe ended up being a hybrid of two other recipes I came across online. I wasn't intending to do this. The plan had been to just make the brie en croûte recipe I found on Food52. I didn't realize until I was already mostly done cooking the onions that I'd somehow managed to get the wrong tab open and had actually been following a completely different baked brie recipe on Eipcurious. So, from there I just kind of improvised to merge the two recipes into something delicious.

Onion and Mushroom Brie en Croûte

Ingredients

Onions

• 2 Tbsp. unsalted butter
• 4 onions, sliced
• 1 tsp. dried thyme
• 1 tsp. coarse sea salt
• few grinds black pepper
• 1 Tbsp. dry white wine
• 1/2 Tbsp. sugar

Mushrooms

• 1 Tbsp. unsalted butter
• 227g cremini mushrooms, sliced
• 4-6 cloves garlic, minced
• 1 Tbsp. dry white wine
• 1 tsp. light soy sauce
• 2 Tbsp. balsamic vinegar

Everything Else

• 454g puff pastry, divided
• 2 small (4-5"/10-13cm) wheels of brie
• 1 egg white
• 1 Tbsp. water

Directions

1. Melt 2 Tbsp. butter over medium heat.
2. Add onions and cook until softened.
3. Add thyme and salt, reduce heat to medium low, and cook, stirring often, until nicely brown and caramelized. This will take about half an hour.
4. Add pepper and cook for another minute or so.
5. Add wine, stir and cook for another minute.
6. Stir in sugar and cook for a further 2 minutes.
7. Remove onions from pan and set aside.
8. Increase heat to medium and add remaining butter to pan.
9. Add mushrooms and garlic and cook until mushrooms release their liquid.
10. Pour wine, soy, and vinegar over mushrooms and cook until liquid has evaporated and mushrooms are nicely glazed.
11. Preheat oven to 425°F (210°C).
12. My puff pastry came in 2 squares, each one pretty much the perfect size for wrapping one of my wheels of brie. If yours are packaged/portioned differently or if you're making your pastry from scratch, you'll have to roll it out to an appropriate size.
13. Line a baking sheet with parchment paper.
14. Place a square of pastry on the lined baking sheet.
15. Bisect each wheel of brie horizontally.
16. Place the bottom half of the brie in the centre of the pastry.
17. Spread half the mushrooms over the brie.
18. Spread about a quarter of the onions on top of the mushrooms.
19. Place the top half of the brie over this.
20. Spread another portion (about 1/3 of the remaining onions) on top of the brie.
21. Mix the water with the egg white.
22. Gently pull the pastry up over the brie stack. Brush a little of the egg wash over the corners to help them stick. Press gently to seal.
23. Entire assembly can be frozen at this point for later baking.
24. Brush the outside liberally with more egg wash.
25. Repeat procedure with second portion of pastry and brie, using up the remaining mushrooms and onions.
26. Bake at 425°F (210°C) for 25 minutes.
27. Serve warm on its own or with baguette and/or crackers.