Heat oven to 425°F. In medium bowl, cut shortening into flour and salt, using pastry blender or crisscrossing 2 knives, until particles are size of small peas.
Sprinkle with cold water, 1 tablespoon at a time, tossing with fork until all flour is moistened and pastry almost cleans side of bowl (1 to 2 teaspoons more water can be added if necessary).
Gather pastry into a ball. Divide pastry in half and shape into two flattened rounds on lightly floured surface.
Roll pastry into circle 2 inches larger than upside-down 9-inch pie plate with floured rolling pin. Fold pastry into fourths; place in pie plate. Unfold and ease into plate, pressing firmly against bottom and side.
In large bowl, mix sugar, cornstarch and cinnamon. Gently stir in blueberries and raspberries. Spoon berry mixture into pastry-lined pie plate.
Sprinkle with lemon juice.
Cut butter into small pieces; sprinkle over berry mixture.
Roll second round of pastry; cut into strips 1/2 to 1 inch wide. (Use a pastry wheel for decorative strips.)
Place 5 to 7 strips across filling in pie plate. Weave a cross-strip through center by first folding back every other strip going the other way. Continue weaving until lattice is complete, folding back alternate strips each time cross-strip is added. (To save time, do not weave strips. Simply lay second half of strips across first strips.) Trim ends of strips. Fold trimmed edge of bottom pastry over ends of strips, building up a high edge. Seal and flute.
Cover lattice top with aluminum foil to prevent excessive browning; remove foil for last 10 minutes of baking.
Bake 50 to 60 minutes or until crust is golden brown and juice begins to bubble through lattice crust.
