Using a mandoline or vegetable peeler, peel one of the zucchinis into thin strips (a peeler will work, a mandoline will be prettier). Place in colander and sprinkle with salt (letting the zucchini release water now will prevent it from waterlogging your tart while baking).

Melt butter in a frying pan over medium heat. Add leek and cook for five minutes. Add diced zucchini and squash, season with salt and pepper, and cook until soft and golden, 12 to 15 minutes. It does not need to be falling apart.

Preheat oven to 375 degrees Fahrenheit.

Line a quarter baking sheet first with aluminum, overhanging on each side (leave it overhanging), and then with Gefen Parchment Paper on top. Roll out puff pastry dough to a little larger than the pan and press into the pan. Add zucchini mixture. Sprinkle with cheese. Whisk together eggs and cream and pour evenly over the tart.

Rinse salted zucchini, then, using paper towels, press it to release as much water as possible. Layer zucchini strips over tart.

Bake for 30 to 35 minutes, until custard is set. About 2/3 through the baking, check crust and tent it with the overhanging foil if it’s golden before the custard is set.