Heat the oven to 425°F, fit the crust into a 9-inch pie plate and crimp the edge.
Peel, core and slice the apples 1/4 inch thick, then toss them with the lemon juice, granulated sugar, 3 tbsp flour, cinnamon, nutmeg and salt.
Mound the apples in the crust, pressing them gently to remove large air gaps.
Rub the 3/4 cup flour, brown sugar and butter together until clumps form, fold in the pecans and scatter the mixture over the apples.
Set the pie on a foil-lined sheet pan and bake for 20 minutes.
Lower the oven to 375°F, shield the edge if it is darkening and bake until thick juices bubble near the center, 40 to 45 minutes more.
Cool for at least 3 hours before slicing so the filling can set.