In a medium pot, whisk together the sugar, cornstarch, and nutmeg.
Add the water, vanilla, and lemon juice and whisk to combine.
Add the blueberries and stir to combine, cooking on medium heat until thick.
Set in a bowl to cool and then put in fridge overnight.
The next day, put the filling in a pie crust and bake for 55-60 minutes at 350°F. (For mini tarts, bake at 400°F for 18-20.)