Trim tough end off asparagus spears (try to keep spears similar lengths). Blanch asparagus in boiling water for 2 minutes. Then place immediately in ice water. (this will brighten the color and help the asparagus be crisp-tender when baked.)
Preheat oven to 400 degrees Fahrenheit. Thaw puff pastry according to manufacturer’s directions. Open pastry and roll out on a lightly floured board. Roll it so it’s approximately a 10 x 16 inch rectangle.
Move pastry dough to baking sheet and score a 1-inch border around the edges with a small sharp knife. Prick the pastry all over (inside the score line) with a fork. Bake about 10 minutes and let cool.
Mix the cheese, parsley, egg, milk, ¼ teaspoon pepper in a medium bowl to combine. Spread the cheese mixture over the puff pastry inside the border.
Toss asparagus with olive oil, ½ teaspoon garlic salt and ¼ teaspoon pepper to coat. Arrange the asparagus end to tip across the puff pastry. Trim any pieces that are too long. The tart looks best with same-length asparagus spears.
Bake 15 minutes or until edges of pastry are golden brown. Remove from oven and sprinkle lightly with lemon zest.
We like this best warm. But you can serve it warm or room temperature.