Preheat oven to 400°F.
On lightly floured surface with lightly floured rolling pin, roll 1 pastry round into a 12-in. circle.
Fit into a 9-in. pie plate, letting edges overhang.
Bend a clean 6-in. square of cardboard in middle forming a wedge. Place in upper left corner of pie (like hands of a clock pointing to 9 and 12).
Fill with blueberry pie filling.
Spoon cherry pie filling into rest of pie. Lift out cardboard.
Roll other pastry round into a 10-in. circle. With a pastry wheel or knife (I used a garnish knife) cut round in five 1/2-in.-wide strips.
With cookie cutter, cut 5 or 6 stars from rest of pastry
Brush strips and stars with beaten egg; sprinkle with sanding sugar.
Starting in middle of pie, carefully place three long strips, evenly spaced, across filling toward bottom edge.
Cut remaining 2 strips into 4-in.-long pieces.
Lay over cherry filling on upper right corner.
Press ends of strips into edge of crust. Roll overhang of bottom crust up over ends of strips to form an even rim.
Flute or crimp rim (I use a fork). Brush rim with beaten egg; sprinkle with sugar.
Place stars on upper left corner of pie (on blueberry filling).
Bake 30 minutes in the center of the oven. I place a aluminum foil covered baking sheet on the rack below to catch any juice the bubbles over.
Reduce heat to 350°F; bake 25 to 30 minutes longer until pastry is golden brown and filling bubbles.
Place on wire rack and cool completely.
Cut into slices and serve warm or at room temp.