This appealing savory tart pairs cheese, potatoes, and thyme on a delightfully crunchy puff pastry foundation. The secret to its simplicity is utilizing ready-made puff pastry and a hint of Dijon mustard, making the tart an easy affair for a busy weekday meal, yet sophisticated enough to impress guests. Serve it as an elegant appetizer cut into 16 slices or as the main course for a light lunch or vegetarian holiday dish when sliced into larger portions.

The tart's crispiness is ensured by a few essential steps in the preparation process. Precooking or par-baking is typically done to fend off any sogginess in tarts or pies. This becomes especially crucial when the filling consists of custard or relatively moist ingredients. With this recipe, though, we bypass the need for par-baking by cleverly using the cheese as a shield between the pastry base and the pre-cooked potato topping.

Also pivotal is the act of pricking the puff pastry. Known as docking, this step aids steam in escaping and prevents the formation of large bubbles, resulting in a layer of beautifully flaky pastry. This is particularly ideal for the edges of a tart such as this one. Be cautious while boiling the potatoes for the first time, as it's crucial that they are only cooked till they're just tender and not too soft. Overcooked potatoes can be problematic to slice.

The act of caramelizing the onions in Step 2 should be done carefully. Make sure to let the condensed droplets fall back into the onions each time you open the lid to stir. This is key to retaining the heat and steam, resulting in faster caramelization.

Helpful time-saving tips include shredding the cheese ahead of time and storing it in a ziplock bag, or parboiling the potatoes up to three days in advance. Just make sure they're completely cooled before refrigerating. When you're ready to assemble the tart, simply peel and slice the potatoes, and follow the recipe. If you choose to prepare the tart ahead of time, wrap it in plastic and store it in the refrigerator for up to three days, then warm it up in an air fryer or preheated oven at 400°F when ready to serve.

Whether you're a culinary novice or a seasoned home cook, this savory tart recipe is a delight to prepare and even more of a pleasure to taste. Serve it at your next gathering to impress your guests with your pastry prowess.