Serves 6 to 8.
Thawing the frozen puff pastry in the refrigerator overnight will help prevent cracking while unfolding it. Be sure to use a low-moisture supermarket mozzarella sold in block form, not fresh water-packed mozzarella. If you prefer to do some advanced preparation, the tart shell can be prebaked through step 1, cooled to room temperature, wrapped in plastic wrap, and kept at room temperature for up to two days before being topped and baked with the mozzarella and tomatoes.
unbleached all-purpose flour for work surface
1 box frozen puff pastry (Pepperidge Farm, 1.1 pound), thawed in box in refigerator overnight
1 large egg , beaten
2 ounces grated Parmesan cheese (about 1 cup)
1 pound plum tomatoes (about 3 to 4 medium), cored and cut crosswise into 1/4-inch-thick slices
2 medium cloves garlic , minced or pressed through garlic press (about 2 teaspoons)
2 tablespoons extra-virgin olive oil
Ground black pepper
8 ounces whole-milk mozzarella cheese , shredded (2 cups)
2 ounces prosciutto , thinly sliced
2 tablespoons chopped fresh basil
1. Adjust oven rack to lower-middle position and heat oven to 425 degrees. Dust work surface with flour and unfold both pieces puff pastry onto work surface. Following the steps* below, form 1 large sheet with border, using beaten egg as directed. Sprinkle Parmesan evenly over shell; using fork, uniformly and thoroughly poke holes in shell. Bake 13 to 15 minutes, then reduce oven temperature to 350 degrees; continue to bake until golden brown and crisp, 13 to 15 minutes longer. Transfer to wire rack; increase oven temperature to 425 degrees.
2. While shell bakes, place tomato slices in single layer on double layer paper towels and sprinkle evenly with 1/2 teaspoon salt; let stand 30 minutes. Place second double layer paper towels on top of tomatoes and press firmly to dry tomatoes. Combine garlic, olive oil, and pinch each salt and pepper in small bowl; set aside.
3. Sprinkle mozzarella evenly over warm (or cool, if made ahead) baked shell. Arrange prosciutto in single layer on top of mozzarella. Shingle tomato slices widthwise on top of prosciutto (about 4 slices per row); brush tomatoes with garlic oil. Bake until shell is deep golden brown and cheese is melted, 15 to 17 minutes. Cool on wire rack 5 minutes, sprinkle with basil, slide onto cutting board or serving platter, cut into pieces, and serve.
*Steps for Puff Pastry
1. Brush egg along one edge of one sheet of puff pastry. Overlap with second sheet of dough by 1 inch and press to seal pieces together.
2. With rolling pin, smooth out seam. Dough should measure about 18 by 9 inches. Use pizza wheel or knife to trim edges straight.
3. With pizza wheel or knife, cut 1-inch strip from long side of dough. Cut another 1-inch strip from same side.
4. Cut 1-inch strip from short side of dough. Cut another 1-inch strip from same side. Transfer pieces of dough to parchment-lined baking sheet and brush with egg.
5. Gently press long strips of dough onto each long edge of dough and brush with egg. Gently press short strips of dough onto each short edge and brush with egg.
6. With pizza wheel or knife, trim excess dough from corners.