Flaky puff pastry squares filled with slow-cooked jammy onions, thyme and a splash of balsamic, topped with nutty Gruyère and baked puffed and golden.
Assemble on the sheets, freeze until firm, and bag; bake from frozen, adding 5 minutes. Swap the Gruyère for goat cheese or blue cheese for a sharper bite.
Caramelize the onions up to 5 days ahead and refrigerate.
Ingredients
Scale
Measurement units
- 2 sheets frozen puff pastry
- 3 yellow onions
- 4 oz Gruyère cheese
- 2 tbsp unsalted butter
- 1 large egg
- 2 tsp fresh thyme leaves
- 1 tsp balsamic vinegar
- ½ tsp kosher salt
- ¼ tsp black pepper
- ½ tsp flaky sea salt
Ingredients
Scale
Measurement units
- 2 sheets frozen puff pastry
- 3 yellow onions
- 4 oz Gruyère cheese
- 2 tbsp unsalted butter
- 1 large egg
- 2 tsp fresh thyme leaves
- 1 tsp balsamic vinegar
- ½ tsp kosher salt
- ¼ tsp black pepper
- ½ tsp flaky sea salt
Instructions
Caramelize the onions
Melt unsalted butter (2 tbsp) in the skillet over medium-low heat, add yellow onions and kosher salt (½ tsp), and cook, stirring often, until deep golden brown and jammy, about 35 minutes.
Stir in fresh thyme leaves (2 tsp), balsamic vinegar (1 tsp) and black pepper (¼ tsp) for about 1 minute.
Equipment: large skillet
Cool the onions
Spread the onions on a plate to cool for 10 minutes while the oven heats to 400°F.
Cut and score the pastry
Unfold frozen puff pastry (2 sheets) onto the lined baking sheets and cut each sheet into nine squares, spacing them apart, about 3 minutes.
Score a thin border inside the edge of each square without cutting through, and prick the centers with a fork, about 2 minutes.
Brush the borders with the beaten large egg, about 2 minutes.
Equipment: two rimmed baking sheets, parchment paper
Top and bake
Spoon the cooled onions into the center of each square and top with Gruyère cheese (4 oz), about 3 minutes.
Bake until the borders are puffed and deep golden and the cheese is bubbling, about 18 minutes.
Sprinkle with flaky sea salt (½ tsp) and serve warm.
Equipment: two rimmed baking sheets
Tomorrow's Meal
Onion Square Breakfast Stacks
Leftover squares recrisped in a dry skillet and topped with a soft fried egg and a few arugula leaves for a quick savory breakfast.
Quick overview:
- 1.Warm leftover squares in a dry skillet over medium-low heat, covered, until the pastry recrisps and the cheese softens.
- 2.Move them to plates.
- 3.Fry eggs in a little butter in the same pan.
- 4.Top each square with an egg and a few arugula leaves.
Before you cook
Cook notes
- • Caramelize the onions up to 5 days ahead and refrigerate.
- • Assemble on the sheets, freeze until firm, and bag; bake from frozen, adding 5 minutes.
- • Swap the Gruyère for goat cheese or blue cheese for a sharper bite.
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