Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
Roll out the chilled pie crust on a lightly floured surface into a 12-inch circle. Transfer it to the prepared baking sheet and chill in the fridge for about 10 minutes to relax the dough.
While the crust chills, slice the heirloom tomatoes into thick rounds and let them sit on a paper towel to drain excess moisture—this helps prevent sogginess.
Remove the crust from the fridge and brush the surface lightly with a bit of olive oil, especially around the edges to promote browning.
Layer the tomato slices over the chilled crust in overlapping circles, starting from the outside and working inward, leaving about a 1-inch border.
Sprinkle the chopped basil evenly over the tomatoes, then scatter the grated Gruyère and Parmesan cheeses on top for a savory, melty layer.
Drizzle the tart with a bit of olive oil and sprinkle generously with salt and freshly ground pepper, enhancing the flavors.
Place the tart in the preheated oven and bake for about 35-40 minutes, until the crust is golden brown and the cheese is bubbly and slightly browned.
Once baked, remove the tart from the oven and let it rest for 5 minutes—this helps the juices settle and makes slicing easier.
Optional: Drizzle a small amount of balsamic vinegar over the top for a smoky-sweet flavor contrast before slicing.
Slice the tart into wedges, serve warm or at room temperature, and enjoy the crackly crust with juicy, flavor-packed tomato layers inside.
