Sublime Apple Crumb Pie

1/2 cup plus 2 Tbsp all-purpose flour

1/3 cup packed light-brown sugar

1/3 cup granulated sugar

1 tsp ground cinnamon

1/2 cup walnuts, coarsely chopped

1 stick (1/2 cup) cold butter, cut in small pieces FILLING

7 medium to large tart apples (about 31/4 lb), such as Granny Smith, Pippins or Greenings

1 Tbsp lemon juice

1/2 cup granulated sugar

3 Tbsp all-purpose flour

1/2 tsp ground cinnamon

1/8 tsp ground nutmeg Garnish: confectioners sugar