Heat oven to 450°F. In saucepan, heat soup, beer and dry potato mix over medium heat until thickened.
Remove pie crusts from pouches; unroll onto 2 ungreased cookie sheets. Spoon 1 cup mashed potatoes on center of each crust, spreading to within 2 inches of edge. Top with soup mixture, dividing evenly between crusts. Fold crust over edge to form 2-inch border, pleating crust as necessary. Brush crust with beaten egg.
Bake 20 to 25 minutes or until crust is golden brown. Garnish with rosemary.