Preheat the oven to 350 degrees F.
Line the mini pie crusts with parchment paper or paper muffin cup liners and fill with dried beans or pastry weights. Place on a baking sheet and bake until set, golden around the edges and on the bottom, and almost completely cooked, about 15 to 20 minutes. Remove from the oven and remove the paper and weights and set aside to cool.
In a mixing bowl, whisk the egg yolks, sugar and salt until mixture is pale yellow, smooth and thick. In a separate bowl, whisk a small amount of the cream into the cornstarch until smooth. Add the remaining cream and whisk to combine. Add the cream mixture to the egg mixture, whisking until the sugar is completely dissolved. Divide the mixture between the pre-baked pastry shells, about 2 tablespoons per pie shell. Bake until the custard is set around the edges but still slightly jiggly in the center, about 20 minutes. Remove from the oven and allow to cool to room temperature before serving. Sprinkle with confectioners' sugar and cinnamon before serving, if desired.
