Cream the butter and sugar together with a hand mixer until smooth.
Add the flour, cornstarch, and salt, and mix until a dough forms.
Press the dough evenly across the bottom of a buttered 5×5-inch baking dish.
Bake the crust for 18 to 20 minutes, until lightly golden, then let it cool.
Make the blueberry filling
Stir the blueberries, sugar, flour, lemon zest, and lemon juice together in a small bowl.
Spoon the berry mixture evenly over the cooled crust.
Set the dish on a baking sheet and bake for 45 to 50 minutes, until the filling bubbles across the surface.
Let the pie cool for at least a few hours so the filling sets before serving.
Video
Notes
Use the right dish size: A 5×5-inch baking dish gives the right crust-to-filling depth. If you don't have one, use a dish with a similar capacity, like a 4×6-inch, so the crust stays thick enough and the filling doesn't bake too shallow.Soften the butter, don't melt it: It should be cool but give when pressed, holding an indentation. Melted butter won't cream with the sugar, and the crust bakes greasy instead of tender.Taste the berries and adjust the sugar: Blueberries swing in sweetness through the season. Taste a few first, then add a little more sugar if they're tart or a little less if they're already sweet.Watch for bubbling across the whole top: The filling is done when it bubbles across the surface, not only at the edges. That's the sign the flour has thickened the juices. If the top browns a little before then, that's fine.Thaw and drain frozen berries: Fresh blueberries are best, but frozen work if you thaw and drain them first. Otherwise the liquid they release makes the filling runny.To double the recipe, double the ingredients and bake in a 6x8 inch baking dish.