Blueberry Chiffon Mini Pies

Preheat oven to 400°F. Unroll 1 piecrust on a lightly floured surface; roll into a 12-inch circle. Using a 6-inch round cutter, cut out 2 circles. Reroll scraps once; cut out 1 more 6-inch circle. Repeat procedure with remaining piecrust for a total of 6 mini dough circles. Fit each circle into a 5-inch round miniature pie pan; fold edges under, and crimp. Prick bottoms and sides with a fork. Chill 15 minutes. 

Place pie pans on a large baking sheet. Line each crust with a small square of parchment paper, and fill with pie weights or dried beans. Bake in preheated oven until crust is set and edges are lightly browned, 12 to 15 minutes. Carefully remove weights and parchment, and continue baking until crusts are golden brown, 4 to 5 minutes. Transfer pie pans to wire racks, and let cool completely, about 15 minutes. 

Meanwhile, process blueberries and lemon juice in a blender or food processor until completely smooth, about 1 to 2 minutes. Combine blueberry mixture and gelatin in a small saucepan over medium-low. Cook, stirring constantly, until gelatin has completely dissolved, about 4 minutes. Transfer mixture to a large bowl, and let stand until room temperature, about 30 minutes. Gently stir mascarpone cheese and ¼ cup of the sugar into blueberry mixture until well combined. 

Beat 1 ½ cups of the heavy cream and 1 teaspoon of the vanilla with a stand mixer fitted with a whisk attachment on medium speed until foamy, about 30 seconds. Increase speed to medium-high, and gradually add ¼ cup of the sugar, beating until stiff peaks form, about 1 minute. Gradually fold whipped cream into blueberry mixture. Spoon mixture evenly into prepared piecrusts (about ¾ cup per pie). Cover and chill at least 4 hours or overnight (about 8 hours). 

Beat remaining ½ cup heavy cream and ½ teaspoon vanilla with a stand mixer fitted with a whisk attachment on medium speed until foamy, about 30 seconds. Increase speed to medium-high, and gradually add remaining 1 tablespoon sugar, beating until stiff peaks form, about 1 minute. Dollop or pipe whipped cream on top of pies. Garnish with blueberries, if desired.