- 2 tablespoons of starch is about what you'd use for an apple pie. you'd have to at least double that for something as watery as raspberries. i'd probably go with a heaping 1/4 cup.
- cornstarch gives a nicer, more transparent product than flour, but it's quirky. i seem to recall that its thickening strenght is affected by acidity. you can substitute flour or quick tapioca for more surefire results.