Heat the oven to 400 degrees. Unroll 1 pie crust on a work surface. Pat out to an 11-inch circle. Cut 12 (2 1/2-inch) circles from the dough. Fit in 12 miniature muffin cups and press in the bottom and sides. Repeat with the remaining pie crust. Bake the crusts for 10 minutes. In the meantime, in a medium bowl, beat the pumpkin, granulated sugar, evaporated milk, egg and pumpkin pie spice until smooth. Remove the crust from the oven. Spoon a rounded tablespoon of the mixture in each crust. Bake on the bottom rack for 13 to 18 minutes or until golden brown and knife inserted in the center comes out clean. Cool in the pan for 10 minutes. Carefully remove to a cooling rack. Cool completely (about 1 hour). Meanwhile, in small bowl, mix the sour cream and powdered sugar. Spoon a small dollop of the sweetened sour cream on each tartlet just before serving. Store in the refrigerator.