Spring Asparagus-Parmesan Tart

Instructions

1. Shred 1/4 cup parmesan. Finely shred remaining parmesan.
2. Melt butter in a large, heavy skillet over medium heat. Add onion, salt and pepper; cook for 10 minutes, stirring frequently. Reduce heat to medium-low. Cook for 20-25 minutes longer or until onion is golden brown, stirring occasionally.
3. Gradually stir in cream. Bring just to a boil; cook and stir until cream is reduced and thickened. Remove from the heat. Stir in shredded parmesan until melted; set aside.
4. Heat oven to 425°F. Line a 15 x 10-inch baking pan with parchment paper.
5. Unfold puff pastry on a lightly floured surface; roll out into a 15 x 10-inch rectangle. Transfer pastry to prepared pan. Score a 1/2-inch border on edges of pastry with a knife. Prick pastry with a fork.
6. Spoon reserved onion mixture to edges of scored pastry. Arrange asparagus and tomatoes on top.
7. Bake for 18-20 minutes or until pastry is golden brown. Sprinkle with finely shredded parmesan. Cool on a wire rack for 10 minutes.
8. Sprinkle with lemon zest just before cutting. Serve warm or at room temperature.