Combine sugar, flour, salt, and spices in a large mixing bowl; stir well. Add 1/4 cup butter, pumpkin, and molasses, beating well. Add eggs, one at a time, beating well after each addition. Stir in milk. Pour mixture into tart shell.
Bake at 350° for 1 hour and 10 minutes. Cool to room temperature. Chill.
Combine brown sugar and 2 tablespoons butter in a small skillet. Cook over medium heat until bubbly. Add pecans; cook an additional 2 minutes, stirring constantly. Remove from heat, and pour mixture onto a sheet of aluminum foil. Cool. Break into pieces.
Garnish tart with whipped cream; sprinkle with praline mixture before serving. Serve cold.