Combine the flour, baking powder, baking soda, and ¾ tsp. salt
Whisk together flour, baking powder, and ¾ teaspoon salt in a bowl, then cut in the butter (cut the butter into slices or cubes, then mix in with a pastry blender or your fingers until the mixture resembles sand). Add the buttermilk and stir until the mixture forms a ball.
Divide dough in half and roll out 1 half to a 12 inch round and transfer the round to a 9 inch glass pie plate (I rolled out on silpat, then used the silpat to transfer to the pie plate. This dough is softer and stretchier than regular pie dough-- you can also try rolling out between 2 sheets plastic wrap).
Preheat oven to 400°F with rack in middle.
Slice tomatoes to about ¼ inch thick. Cut the corn off the cob. Combine the mayonnaise and the lemon juice in a small bowl.
Arrange half of tomatoes in crust, overlapping, and sprinkle with half of corn, half of thyme, a generous pinch of salt and a grinding of black pepper. Repeat with the remaining tomatoes, corn and seasonings, then top the whole shebang with 1 cup of grated cheese.
Pour lemon mayonnaise over filling and sprinkle with remaining cheese.
Roll out remaining crust to about a 12 inch round, then drape it over the pie, and pinch the crust to form a seal. Cut steam vents in top crust and brush crust with melted butter.
Bake 30-35 minutes until the crust is golden, then cool on a rack. Serve warm.
Notes
Adapted from Gourmet Magazine
Recipe by The Domestic Front at http://www.thedomesticfront.com/corn-and-tomato-pie-summer-in-a-crust/