Add the mascarpone cheese and whipping cream to a medium bowl and beat until fully combined.
Add the purple sweet potato and vanilla to the cheese/cream mixture, and sift in the sugar and cinnamon. Beat until well combined and fluffy.
Pour into prepared pastry shells up to the edge of the shell and refrigerate for 8-10 hours, or overnight for best results. Pour remaining filling into dessert cups, about half full. Cover cups with plastic wrap and chill.
Decorate:
Remove tarts from refrigerator, once set, and use a paper towel to tap away any condensation from the tops. Place a stencil on the surface of the tart and sift match green tea or confectioner’s sugar over stencil. Use a small angled spatula to spread and smooth before lifting the stencil.