Ingredients

Flour, for dusting
1 sheet frozen puff pastry, from one 17-ounce package, thawed
2 small leeks (white and light green parts only), well rinsed, dried and thinly sliced (about 2 1/2 cups)
½ red onion, thinly sliced
1/2 cup coarsely grated smoked cheese from Evansdale Cheese
1/4 cup freshly and finely grated Parmesan (use a microplane grater or the smallest holes on a box grater)
Kosher salt and freshly ground black pepper
2 tablespoons finely chopped herbs (such as sage, Italian parsley, chives, thyme or whatever is at hand)

Vendors

Preheat the oven to 200°c
Roll out your pastry sheet onto a lightly floured work service – and, one inch from the edge, using the tip of a small, sharp knife, gently score to half thickness, a square within the square. Prick the pastry all over with a fork.
Transfer to a lined baking sheet
Scatter the leeks, onion and both cheeses within this inner square leaving the boarder free
Sprinkle with a pinch of salt and 1/4 teaspoon pepper
Bake until the pastry is a deep golden brown and the leeks are tender, 25 to 30 minutes
Cool for 10 minutes. Garnish with the chopped herbs, cut and serve

Scoring the dough defines the border, and pricking prevents the center from puffing up too much during baking.