1. Place a rack in the center of the oven and preheat the oven to 375°F.
2. Open the package of crescent roll dough and separate it into 8 triangles. Arrange the triangles in a 10-inch tart pan or pie pan with the long points toward the center so that the bottom and side of the pan are covered with dough. Press the edges of the dough triangles firmly together to seal them. Bake the crust until it is lightly browned and puffed, 8 minutes.
3. Meanwhile, cut the tomatoes in half (slice cherry tomatoes crosswise and grape tomatoes lengthwise).
4. Remove the tart pan from the oven; leave the oven on. Press down on the crust with the back of a spoon to flatten it. Arrange the tomatoes, cut side up, on the bottom of the crust, completely covering it. Drizzle the olive oil over the tomatoes, sprinkle them with salt, then scatter the basil evenly over the top. Crack the eggs into a small bowl, add the cream and mozzarella cheese, and whisk to combine. Pour the egg mixture over the tomatoes.
5. Bake the tart until the custard has set and the crust is a deep golden brown, 18 to 20 minutes. Remove the tart from the oven and place it on a wire rack to cool, 5 minutes, then slice the tart and serve it.
• The most efficient way to slice basil leaves is to stack them, roll them into a cigar shape, then slice them crosswise. This creates basil slivers, or a chiffonade, as it is called in French.
• You can add slices of garlic to the tomatoes if the mood hits you.
• If you use half Parmesan and half mozzarella cheese, the tart will have a richer flavor and the top will be browner.