Ice creams with a high water content, such as fruit flavors, will freeze icy. To improve the texture, add light corn syrup—not the maligned high-fructose variety, but rather the bottled supermarket stuff that's only one-third as sweet as table sugar. If you can't abide by corn syrup, glucose or tapioca syrup fill similar roles. Just avoid honey, maple, and agave nectar, which are all sweeter than table sugar and won't bring the viscosity you need. For the fruit, buy the finest peak-season raspberries you can find and leave them raw to preserve their fresh, ripe flavor. Don't shy away from salt either, which will help keep the raspberry essence from being lost in the cream. An equal weight of blueberries or strawberries works just as well.