From America's Test Kitchen: "This recipe was developed using fresh blueberries, but unthawed frozen blueberries (our favorite brands are Wyman’s and Cascadian Farm) will work as well. If using frozen berries, in steps 16 & 17, cook half the frozen berries over medium-high heat, without mashing, until reduced to 1 1/4 cups, 12 to 15 minutes. Grind the tapioca to a powder in a spice grinder or mini food processor. If using pearl tapioca, reduce the amount to 5 teaspoons. Vodka is essential to the texture of the crust and imparts no flavor; do not substitute." Cook time includes chill times.