How to Make It
Preheat oven to 400°F. Unroll piecrust, and place in a 9-inch pie plate; flute edges.
Process tapioca, lavender, salt, and 1/2 cup of the brown sugar in a food processor until thoroughly combined and finely ground, about 1 minute.
Toss together blueberries and brown sugar mixture in a large bowl. Gently stir in blueberry preserves and lemon juice until thoroughly combined. Spoon mixture into prepared pie plate. Stir together almonds, flour, and remaining 3/4 cup brown sugar in a medium bowl; stir in melted butter until thoroughly combined. Sprinkle almond mixture over blueberry mixture.
Bake in preheated oven 15 minutes. Cover pie with aluminum foil, and bake until top is golden brown and pie is bubbling, 40 to 45 minutes. Transfer to a wire rack, and cool completely, about 3 hours.