Hi Jude - There are at least 3 ways to thicken pies, that I know of - flour, cornstarch and my favorite is Minute Tapioca. Certain pies seem to call for the different methods - my mother (and I) always used flour when we make apple or rhubarb pies, but for fruit pies like raspberry or blueberry, I have always used Minute tapioca, following the directions on the side of the box for the quantities.

The Minute tapioca makes a nice clear gel, vs. a more cloudy thickening with flour. I've never used cornstarch, although I know you can (also arrowroot)

Hope this helps you and I have to tell you how jealous I am that you're making raspberry pies - MY FAVORITE! I was born and raised in Upper Michigan and my mom had a big raspberry patch and there is nothing more wonderful smelling or tasting than a fresh raspberry pie! When I have to pay $6.00 for a tiny little container of raspberries in the store, I certainly don't make them anymore. It's comfort food for me!

Good luck -

June