From America's Test Kitchen Season 9: The Best Blueberry Pie
If the filling in blueberry pie doesn’t jell, a sliced wedge can collapse into a soupy puddle topped by a sodden crust. Too much thickener and the filling can be so dense that cutting into it is like slicing through gummi bears. We wanted a pie that had a firm, glistening filling full of fresh, bright flavor and still-plump berries.
To thicken the pie, we favored tapioca because it didn’t mute the fresh yet subtle blueberry flavor as cornstarch and flour did. The back of the tapioca box recommended 6 tablespoons, but this produced a stiff, congealed mass. Cooking and reducing half of the berries helped us cut down on the tapioca required, but not enough. A second inspiration came from a peeled and grated Granny Smith apple. Apples are high in pectin, a type of carbohydrate that acts as a thickener when cooked. Combined with a modest 2 tablespoons of tapioca, the apple thickened the filling to a soft, even consistency that was neither gelatinous nor slippery. The crust posed a much simpler challenge. As with all of our fruit pies, baking on a preheated baking sheet on the bottom oven rack produced a crisp, golden bottom crust. And we found a fast, easy alternative to a lattice top in a small biscuit cutter, which we used to cut out circles in the top crust before transferring the dough onto the pie. The attractive, unusual-looking top crust vented the steam from the berries as successfully as a classic lattice top.
Makes one 9-inch pie
This recipe was developed using fresh blueberries, but unthawed frozen blueberries (our favorite brands are Wyman’s and Cascadian Farm) will work as well. In step 4, 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.