Combine brown sugar, gelatin, salt, cinnamon, nutmeg, and ginger in a heavy saucepan. Combine egg yolks and milk; beat well. Stir egg mixture into brown sugar mixture. Cook over medium heat, stirring constantly, until mixture comes to a boil. Remove from heat; stir in pumpkin. Chill until mixture begins to thicken.
Beat egg whites (at room temperature) until foamy. Gradually add 1/3 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Fold egg whites into chilled pumpkin mixture. Pour filling into pastry shell. Chill. Garnish with whipped cream and pecans before serving.