Bumbleberry is a combination of berries. Sometimes chopped apples and rhubarb are added to the filling. Use whatever combination you like as long as the fruit equals 4 cups.
Double pie crust (homemade or store bought)
1 1/3 cups fresh raspberries*
1 1/3 cups fresh blueberries*
1 1/3 cups fresh blackberries*
1 cup granulated sugar
2 tablespoons fresh lemon juice
1/3 cup all-purpose flour
2 tablespoons cold unsalted butter, cut into small pieces
1 tablespoon coarse sugar (sanding sugar) or 1 tablespoon granulated sugar
* If you desire to use frozen berries instead, purchase a large bag of frozen mixed berries and use 4 cups.
Find it online: https://simplygreatrecipes.com/bumbleberry-pie/