Preheat oven to 400 degrees.

In a small pan, melt the butter over low/medium heat.

Add the leeks and sauté until they soften but are not browned, about 5 minutes.

Just before removing from heat, add the garlic and stir into the butter and leeks.

Remove from heat and set aside.

Roll out pastry dough to a 12 x 14 rectangle.

Fold edges over to create a border.

Place on sheet pan that has been covered with parchment paper.

Spread the leek and garlic mixture over the dough, inside of the pastry border.

Season with salt and pepper and then sprinkle the cheese on top of the leeks.

Arrange the asparagus spears on top of the tart and season again with a bit of salt and pepper.

Sprinkle the lemon zest over the tart.

Place in oven and bake for 30 minutes or until tart is nicely browned and the asparagus are tender.