Heat oven to 425°F. Set rack in the lower third.
Dust counter with flour. Unroll one crust and fit a 9-inch pie plate.
Chill the lined pan while you mix the filling.
Stir pie filling, cornstarch, lemon juice, almond extract, and salt in a bowl.
Spoon filling into crust. Spread evenly. Dot the top with butter.
Unroll the second crust over the pie. Trim any overhang.
Crimp the edges to seal. Cut several vents on top.
Brush top with milk. Sprinkle generously with coarse sugar.
Bake 20 minutes. Lower oven to 375°F and bake 25–30 minutes more.
Tent edges with foil if browning fast. Bake until bubbling and deep golden.
Cool on a rack at least 3 hours before slicing.