Preheat oven 375F. Brush bottom and sides of crust evenly with egg yolk; bake on baking on baking sheet until light brown ,about 5 minutes. Remove crust from oven.
Combine sliced apples, lemon juice, 1/2 cup sugar, 1/4 cup brown sugar, 3 tablespoons flour, salt, cinnamon and nutmeg. Mix well and spoon into crust.
Mix remaining flour, sugar, brown sugar and butter with fork until crumbly. Sprinkle topping mixture evenly over apples. Bake on baking sheet until topping is golden and filling is bubbling; about 50 minutes. Cool thoroughly on wire rack, at least 4 hours. Serve at room temperature.
