Cream the cream cheese, brown sugar, spices and salt together, in a bowl, until they are light and fluffy, using an electric mixer set on medium speed. Add the eggs, one at a time, beating well after each addition. Blend in the pumpkin, milk, and vanilla. Pour the mixture into the unbaked pie shell. Bake in a preheated 375 degree F. oven for 45 to 50 minutes or until a knife inserted halfway between the edge and center comes out clean. Cool slightly on a wire rack. Meanwhile blend the sour cream and sugar together and spread over the top of the warm pie. Return the pie to the oven and bake an additional 3 to 5 minutes or just until the topping is set. Cool on a wire rack. Cover and chill in the refrigerator before serving.