Pie Crust

1. To assemble the pie crust, cream together the sugar and butter in a stand mixer fitted with a paddle attachment or using a handheld electric mixer. Mix until light and fluffy then add the egg, egg white and vanilla and beat until incorporated (at this point the mixture may look chunky or separated, but stick with the recipe and the dough will come together). Whisk together the flour and salt in a medium bowl then slowly add to the sugar mixture and mix just until the dough forms. Cover with plastic wrap and refrigerate until ready to use, at least 1 hour and up to 1 day ahead of time.

Streusel Topping

1. To make the streusel topping, mix together the flour and sugar in a small bowl and cut in the butter using your hands or a fork until the mixture resembles coarse cornmeal. Set aside (mixture may be made a day ahead of time and stored covered in the refrigerator).

Pie Filling

1. To assemble the pie, stir together the sour cream, sugar, flour, egg yolk and vanilla in a medium bowl until smooth. The mixture may be made a day ahead of time. Store covered in the refrigerator.
2. When ready to bake, preheat the oven to 375°F and place oven racks in the upper and lower thirds of the oven.
3. Divide the cookie pie dough evenly among 8 4- to 5-inch mini pie pans. That should be about 2.2 ounces or 1/4 cup per mini pie. Press the dough into the pan, being sure the dough comes up the edges, but not over the top edge, of each pie pan. Divide the custard evenly into the prepared pie pans, about 1 1/2 tablespoons per mini pie. Now divide the peach slices evenly over the custard, shingling the peach slices. Sprinkle the streusel topping evenly over each pie.
4. Divide the mini pies evenly between two baking sheets and place one on each oven rack. Bake in preheated oven until the custard is set and the crust is golden brown, about 20-23 minutes, rotating and turning the pans halfway through cooking.
5. Remove from the oven and cool at room temperature for 10 minutes in the pans. Gently remove the pies from the mini pans using an offset spatula or a flexible plastic knife. Cool on the wire rack until warm or room temperature, another 10 minutes. Serve warm or room temperature. Transfer to the refrigerator and store in an airtight container for up to 4 days. Do not leave the mini pies out at room temperature for more than 2 hours.