Preparation Whisk together flour, baking powder, and 3/4 teaspoon salt in a bowl, then blend in cold butter (3/4 stick) with your fingertips or a pastry blender until it resembles coarse meal. Add milk, stirring until mixture just forms a dough, then gather into a ball. Divide dough in half and roll out 1 piece between 2 sheets of plastic wrap into a 12-inch round (1/8 inch thick). Remove top sheet of plastic wrap, then lift dough using bottom sheet of plastic wrap and invert into pie plate, patting with your fingers to fit (trim any overhang). Discard plastic wrap. Preheat oven to 400°F with rack in middle. Whisk together mayonnaise and lemon juice. Arrange half of tomatoes in crust, overlapping, and sprinkle with half of corn, 1 tablespoon basil, 1/2 tablespoon chives, 1/2 teaspoon salt, and 1/8 teaspoon pepper. Repeat layering with remaining tomatoes, corn, basil, chives, salt, and pepper, then sprinkle with 1 cup cheese. Pour lemon mayonnaise over filling and sprinkle with remaining cheese. Roll out remaining piece of dough into a 12-inch round in same manner, then fit over filling, folding overhang under edge of bottom crust and pinching edge to seal. Cut 4 steam vents in top crust and brush crust with melted butter (2 teaspoons). Bake pie until crust is golden and filling is bubbling, 30 to 35 minutes, then cool on a rack. Serve warm or at room temperature. Cooks' note:Pie can be baked 1 day ahead and chilled. Reheat in a 350°F oven until warm, about 30 minutes.
Preparation Whisk together flour, baking powder, and 3/4 teaspoon salt in a bowl, then blend in cold butter (3/4 stick) with your fingertips or a pastry blender until it resembles coarse meal. Add milk, stirring until mixture just forms a dough, then gather into a ball. Divide dough in half and roll out 1 piece between 2 sheets of plastic wrap into a 12-inch round (1/8 inch thick). Remove top sheet of plastic wrap, then lift dough using bottom sheet of plastic wrap and invert into pie plate, patting with your fingers to fit (trim any overhang). Discard plastic wrap. Preheat oven to 400°F with rack in middle. Whisk together mayonnaise and lemon juice. Arrange half of tomatoes in crust, overlapping, and sprinkle with half of corn, 1 tablespoon basil, 1/2 tablespoon chives, 1/2 teaspoon salt, and 1/8 teaspoon pepper. Repeat layering with remaining tomatoes, corn, basil, chives, salt, and pepper, then sprinkle with 1 cup cheese. Pour lemon mayonnaise over filling and sprinkle with remaining cheese. Roll out remaining piece of dough into a 12-inch round in same manner, then fit over filling, folding overhang under edge of bottom crust and pinching edge to seal. Cut 4 steam vents in top crust and brush crust with melted butter (2 teaspoons). Bake pie until crust is golden and filling is bubbling, 30 to 35 minutes, then cool on a rack. Serve warm or at room temperature. Cooks' note:Pie can be baked 1 day ahead and chilled. Reheat in a 350°F oven until warm, about 30 minutes.