Preheat oven to 375 degrees. Pour all ingredients for the pie filling into a large bowl. Gently stir to coat raspberries in flour and sugar mixture without breaking them as best as you can. Pour into unbaked pie shell and even out the top.Combine all ingredients for the topping together. Using a pastry cutter, a fork or your fingers, mix butter into flour mixture and break it into small pea-sized pieces. Sprinkle evenly over raspberries. Place pie into preheated oven on middle rack with a baking sheet placed below to catch any drips. Bake for 30 minutes then reduce the heat to 325 and bake another 30 minutes. Remove from oven and cool completely. Serve with whipped cream or vanilla ice cream.