Heirloom tomatoes really DO taste better than their genetically-modified counterparts.
To make the tart: Heat oven to 400. Roll out puff pastry dough to 12"x12", and fold the edges in to make a border. Brush with a very light coating of sour cream, and chill. Then top with a layer of thin tomato slices (about 1/8" thick). Season with salt & pepper. Bake for 20-30 minutes (sprinkle feta on about halfway through), until the dough is done and golden brown. When it's done, top with basil leaves.