Preheat oven to 350 degrees F.

In a large bowl, combine all ingredients for the topping, making sure to break the butter into chunks the size of peas.

Set in the refrigerator to keep cold.

In a separate large bowl, combine the filling ingredients and mix well.

Spoon the filling into a 9 inch pie pan or baking dish.

Sprinkle the topping onto the filling and spread evenly.

Bake in oven for 1 hour.

Allow the plum crumble pie to cool for at least 30 minutes.

Serve with ice cream or cold whipped cream.