Mushroom Onion Squares
These savory little bites make a great party appetizer or afternoon snack. We used brown mushrooms in our version; feel free to use whatever mushrooms (or a combination) you like.
10 minutes
45 minutes
Mushroom Onion Squares
1 tablespoon salted butter, divided
2 tablespoons olive oil, divided
3-4 ounces mushrooms, brushed clean, stemmed and sliced
1 medium yellow or red onion, thinly sliced
Leaves from 1 sprig fresh thyme (optional)
1 teaspoon sugar
1 tablespoon balsamic vinegar
4 ounces Gruyère or Swiss cheese, grated
1 sheet frozen puff pastry, thawed
1 egg, lightly beaten
Salt and pepper, to taste
In a large skillet over medium heat, heat 1 tablespoon of oil along with 1 tablespoon of butter. Add the mushrooms and sauté for about 5 minutes until tender. Remove and set aside in a medium bowl.

Heat the remaining 1 tablespoon of oil sauté the onions for 5 minutes. Add the sugar and continue to cook for 25 minutes on medium low heat, stirring every few minutes. Add the balsamic vinegar and stir gently. remove from heat and add the onions to the mushroom mixture. Season with salt and pepper to taste. Allow to cool to room temperature. Add the cheese and mix well.

Preheat your oven to 400 F. Line a baking sheet with parchment paper or a silicone mat.

Cut the puff pastry into 2 inch squares and place them on the lined baking sheet. Brush the beaten egg on the squares. Place a tablespoon of caramelized onion mixture in the center or each square. Bake for 20-25 minutes until cheese is melted and pastry is brown and puffed. Let cool a few minutes before serving.
Looking for inspiration? Try these recipes:
Carolyn Quilici’s Red Meat Sauce
Carolyn Quilici’s Red Meat Sauce
Braised Beef Short Ribs with Mushrooms and Pearl Onions
Braised Beef Short Ribs with Mushrooms and Pearl Onions
Kerala Prawn Curry
Kerala Prawn Curry