Red Onion, Mushroom and Blue Cheese Tarte Tatin Recipe - Food.com

Ingredients

• 2 red onions, large
• 4 tablespoons olive oil (60 ml)
• 2 tablespoons balsamic vinegar (30 ml)
• 1 tablespoon sugar, dark brown (15 ml, treacle or muscovado sugar)
• 8 ounces white mushrooms, small, cleaned, whole (200 g, and halved if large)
• 1 pinch flaked sea salt
• 2 ounces walnuts (50 g)
• 3 1/2 ounces blue cheese (100 g, your choice, I used Danish)
• 8 ounces puff pastry (250 g, defrosted, cold)
• 1 egg, beaten