Preheat the oven to 425 degrees F (220 degrees C).

Combine frozen blueberries, sugar, cornstarch, lemon juice, and salt in a medium pot. Cook over medium-high heat, stirring often, for 10 to 15 minutes.

Mix flour and salt in a bowl. Cut in ¾ cup butter until mixture resembles coarse crumbs. Gradually add water until dough forms a shapeable ball.

Divide the dough in half. Roll out one portion into a 10-inch circle and transfer to a 9-inch pie dish. Trim and crimp edges.

Pour filling into the prepared pie crust and dot with 1 tablespoon butter.

Roll out the top crust, cut into strips, and weave a lattice pattern on the pie. Fold edges under and flute the crust.

Combine the remaining butter with milk, microwave to melt, and brush over the top crust.