Preheat oven to 375 F. In a bowl, combine the sugar, flour, nutmeg, and salt. Then, add the melted butter and toss to distribute. Add the apples and raisins, stir gently, and pour into the pastry shell. Bake for 20 minutes. Meanwhile, in a small bowl, combine the brown sugar, flour, and cinnamon. Cut in the butter in tiny bits and use your hands or a pastry cutter to incorporate until the butter bits are pea-sized and the mixture resembles coarse sand. Toast the walnuts in the oven on a sheet pan, or over medium-high heat in a dry skillet until they are golden brown and fragrant. Add them to the topping mix. When the pie has been baking for 20 minutes, remove it from the oven, and add the topping. Return it to the oven for another 40 minutes or until golden brown and bubbly.