Cook shallots and red bell pepper in butter in a large skillet over medium-high heat until tender; whisk in flour. Cook 1 minute, whisking constantly. Gradually whisk in milk; cook, whisking constantly, until mixture is thickened and bubbly. Stir in crabmeat and next 5 ingredients. Remove from heat; set aside.
Unfold 1 piecrust; cut crust in half.
Working with half of 1 crust, place sage leaves on 1 side of pastry half; press sage into pastry with a rolling pin. Carefully turn dough over. Place 1/3 cup crabmeat mixture on half of crust side without sage leaves. Brush edges of pastry with water. Fold pastry over filling, and pinch to seal. Trim sealed edges with pastry wheel or pizza cutter. Place on baking sheet lined with parchment paper. Repeat procedure with remaining piecrust, sage, and crabmeat mixture.
Bake at 425° for 20 minutes or until golden.