Trader Joe's Caramelized Onion Feta Pastry Bites

1/2 box Puff Pastry
2 yellow onions
2 tablespoons unsalted butter
2 tablespoons brown sugar
1/4 teaspoon Kosher salt
3 ounces feta cheese
4 tablespoons unsalted butter, melted
1/4 cup sour cream
1 large egg

Preheat the oven to 400 degrees.
Slice the yellow onions thinly and put them in a cast iron skillet with the butter on medium-low heat.
Add salt and brown sugar and cook on low for 15-20 minutes until browned, stirring every few minutes.
In a bowl whisk together the feta, butter, sour cream and eggs.
Unfold the puff pastry rectangles and cut each three piece sheet into 30 squares.
Spray the mini muffin tin with cooking spray and put the puff pastry squares into each well.
Spoon in a scant tablespoon of cheese mixture into each well, then cover with a few pieces of onion.
Bake for 18-20 minutes.
If freezing:
Add the ingredients to the muffin tins and before baking put the trays into the freezer.
From frozen bake 20-22 minutes.