Graham Cracker Crust
9 graham crackers, broken into rough pieces
2 tablespoons granulated sugar
5 tablespoons unsalted butter, melted and warm
2 cups fresh raspberries (about 9 ounces)
2 cups fresh blackberries (about 11 ounces)
2 cups fresh blueberries (about 10 ounces)
½ cup granulated sugar (3 1/2 ounces)
3 tablespoons cornstarch
⅛ teaspoon table salt
1 tablespoon lemon juice from 1 lemon
2 tablespoons red currant jelly
1 cup heavy cream (cold)
1 tablespoon granulated sugar
1 teaspoon vanilla extract
1. FOR THE CRUST: Adjust oven rack to middle position and heat oven to 325 degrees.
2. In food processor, process graham crackers until evenly fine, about 30 seconds (you should have 1 cup crumbs). Add sugar and pulse to combine. Continue to pulse while adding warm melted butter in steady stream; pulse until mixture resembles wet sand. Transfer crumbs to 9-inch glass pie plate; form crust using 1/2-cup dry measuring cup. Bake crust until fragrant and beginning to brown, 15 to 18 minutes; transfer to wire rack and cool completely while making filling.
3. FOR THE FILLING: Combine berries in large colander and gently rinse (taking care not to bruise them); spread berries on paper towel-lined rimmed baking sheet and gently pat dry with additional paper towels.
4. In food processor, puree 2 1/2 cups mixed berries until smooth and fully pureed, about 1 minute. Strain puree through mesh strainer into small nonreactive saucepan, scraping and pressing on seeds to extract as much puree as possible (you should have 1 1/4 to 1 1/2 cups). Whisk sugar, cornstarch, and salt in small bowl to combine, then whisk mixture into puree. Bring puree to boil over medium heat, stirring constantly with wooden spoon; when mixture reaches a boil and is thickened to consistency of pudding, remove from heat, stir in lemon juice, and set aside to cool slightly.
5. While puree is cooling, place remaining berries in medium bowl. Heat jelly in second small saucepan over low heat until fully melted; drizzle melted jelly over berries and toss gently to coat. Pour slightly cooled puree into cooled pie shell; top with fresh berries. Loosely cover pie with plastic wrap; refrigerate until chilled and puree has set, about 3 hours (or up to 1 day).
6. FOR THE WHIPPED CREAM: Just before serving, beat cream, sugar, and vanilla with electric mixer on low speed until small bubbles form, about 30 seconds. Increase speed to medium; continue beating until beaters leave trail, about 30 seconds longer. Increase speed to high; continue beating until cream is smooth, thick, nearly doubled in volume, and forms soft peaks, about 30 to 60 seconds.
7. Cut pie into wedges and serve with whipped cream.