1. Preheat the oven to 350˚
2. To make the crust in the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar until the mixture is light and fluffy. In a separate bowl whisk together the flour and baking powder. Mix the flour mixture into the butter with the mixer on low until dough forms. Pat the dough into a buttered 9-inch tart pan. Bake for 12-15 minutes until lightly golden brown. Let the crust cool completely.
3. To make the filling, in a saucepan over medium heat, whisk together the sugar and cornstarch. Immediately add the milk, egg yolks, butter, and lemon zest, whisking well while adding each to avoid clumps. Cook the mixture, whisking constantly, until it thickens and begins to bubble. Continue cooking and whisking for 2 minutes. Remove the pan from the heat, and whisk in the lemon juice.
4. Let the filling cool to room temperature. Pour it into the crust, and refrigerate the tart for at least 30 minutes.
5. In a medium bowl fold together sour cream and 1 ½ cups of the blueberries. Spread the sour cream and blueberry mixture on top of the lemon curd. Keep the topping refrigerated until you are ready to serve.
6. Top with fresh whipped cream, the remaining ½ cup of blueberries, and lemon zest just before serving.