Preheat oven to 450 degrees. In a medium bowl combine, cherries, sugar, flour, cornstarch, lemon juice, and zest.
On a lightly floured surface, roll one disk of dough out slightly less than 1/8-inch-thick. Use a 4 3/4-inch cutter to cut out 6 rounds. Fit rounds into 3 1/2-inch fluted tart pans with removable bottoms. Divide filling evenly between pans. Roll second disk of dough out 1/8-inch-thick. Use a 3 3/4-inch biscuit cutter to cut out 6 rounds. Place rounds over fruit. Cut vents into each pie. Seal by folding edges over and crimping with thumb and forefinger. Place onto a parchment lined baking sheet.
In a small bowl, whisk together egg and heavy cream. Brush evenly over tops of pies. Bake until golden brown, and juices are bubbling, 35 to 40 minutes. Remove from oven, and let cool for at least 1 hour before serving.