In a small saucepan, add the blueberries and lemon juice. Place over medium heat.
In a small bowl, whisk together the erythritol, starch, and salt. Sprinkle over the blueberries and stir until the mixture is completely coated. Stir occasionally and bring to a boil. Cook until thickened, and when about half of the blueberries have burst, remove from the heat.
Preheat your oven to 350 degrees Fahrenheit, spray a 9” brownie pan with cooking spray, and thaw the pie crusts at room temperature for ~20 minutes.
Unroll one pie crust in the brownie pan and press against the “walls” of the pan so that it sticks. Bake for 14 minutes, or until golden brown.
While that bakes, slice the second pie crust into centimeter-wide strips (I made ½cm strips for extra decoration).
Scoop the blueberry mixture into the pie crust.
Arrange the pie crust strips on top of the blueberry filling to make a lattice. Trim the ends of the pie crust strips so that it fits nicely. Carefully slice the exposed crust “walls” so that it’s level with the filling and lattice.
Bake ~38 minutes, or until the lattice is nicely golden brown and the filling is bubbling. Let cool completely, then cover and refrigerate overnight. Slice the next day, then serve and enjoy!