Remove seeds from plums; cut each in half crosswise. combine plums with dry ingredients, 1/2 c. sugar, 1/4 c. flour, 1/4 tsp. salt, 1/4 tsp nutmeg. Place plum mixture in pastry shell. Add lemon juice.
TOPPING: Cut butter into dry ingredients, 1/2 c. flour, 1/2 c. sugar and 1/2 tsp. cinnamon. Sprinkle over filling. Place pie in large paper bag. Fasten open end by folding over 2 times and stapling 3 or 4 times. Place bag on cookie sheet. Bake 1 hour at 450 dgrees. Remove from oven; leave in bag a few minutes until juice stops boiling. Serve warm or cold.