How to Make It
In a medium bowl, combine the flour with the cornmeal, 2 tablespoons of the sugar and the salt. Add the butter and, using a pastry blender, 2 knives or your fingers, work it into the flour until the mixture resembles coarse meal. Add the water and stir just until a dough forms. Gather the dough together and knead 2 or 3 times.
Roll the dough into a fat log and cut it into 8 equal pieces. On a lightly floured surface, flatten each piece of dough into a 2-inch disk. Wrap each disk in plastic and refrigerate for at least 30 minutes or overnight.
Preheat the oven to 350°. Line a large baking sheet with parchment paper. On a lightly floured surface, roll each disk of dough out to a 6-inch round. In a medium bowl, toss the peaches with the blueberries and the remaining 1/4 cup of sugar. Spoon the fruit onto the dough and fold up the sides, overlapping and crimping as you go. Transfer the tartlets to the baking sheet and bake for 50 minutes, or until the crust is golden and crisp and the fruit is bubbling. Let cool.