2cupsleeks(approximately 1 1/2 - 2 leeks), white and pale green parts only, chopped
1 14-ouncecan quartered artichoke hearts,drained and patted dry
freshly grated parmesan cheese,1/4 cup or to taste
1sheet puff pastry
Heat the butter in a large skillet over low heat. Keep a small cup of water nearby. Add the leeks with a pinch of salt and stir to coat in the butter. Allow the leeks to sweat for 2-3 minutes and then turn up the heat to medium. Allow the leeks to slowly caramelize, stirring frequently. As a brown glaze forms on the bottom of the pan add a 1-2 tablespoons of water at a time and stir to incorporate the glaze back into the leeks. Once they are nicely caramelized (approximately 10-15 minutes), remove from the heat and set aside.
Place the spinach in a large skillet with a splash of water or olive oil (this step can be done in batches if the pan isn't large enough to accommodate all of the spinach). Turn the heat to medium low. Turn the spinach for a few minutes until it wilts. Season with a bit of salt and pepper and allow to drain on a plate with paper towels.
Preheat the oven to 400 degrees F and line a baking sheet with parchment paper. Roll out chilled puff pastry until it is approximately 11x15 inches or 12x14 inches. Place the dough on the prepared baking sheet. Distribute the leeks, spinach and artichokes evenly, leaving a small border around the edge of the dough. Top with parmesan cheese.
Bake the tart for 25-30 minutes, or until the edges are golden and firm. Periodically check on the tart while it's cooking. If part of the dough around the edge inflates with an air bubble at any point, gently prick it with a fork to deflate.
Slice and serve.
If this tart is being prepared for a party, save time by preparing the leeks and spinach in advance. 40 minutes before guests arrive you can roll out the dough, layer the ingredients and bake the tart so it will be ready just in time to serve.Make sure to drain the artichokes and spinach before placing them on the puff pastry dough to avoid excess liquid. This could result in a soggy tart.