Preheat oven to 225 degrees. Melt butter in a 9" baking pan in oven. Add pecans and brown sugar; mix well. Bake for about 45 minutes, stirring every 10-15 minutes. Remove from oven and spread pecans on plate lined with wax paper; set aside.
Set oven on 325 degrees. With an electric mixer, cream sugar and cream cheese until fluffy. Add eggs and beat well. Add pumpkin and spices; beating until well combined. Slowly, beat in evaporated milk. Pour mixture into pie crust and place on lowest oven rack. Due to the amount of liquid and slow cooking temperature, it will require approximately 2 hours for baking time. Insert a toothpick in the center and if it comes out clean, it's done. If the edges of the crust are browning too quickly, cover with foil. As soon as the pie is removed from the oven, arrange pecans on top. Cool (which will take about 2 hours). Refrigerate. Pie freezes well. Top with Cool Whip or sweetened whipped cream before serving, if desired.