Bake pie according to package directions. Cool on wire rack for 30 minutes or until warm.
Invert pie onto an ovenproof serving plate or foil-lined baking pan. Meanwhile, in a small saucepan, melt butter. Add the brown sugar, cream and syrup; cook and stir until smooth. Stir in the cranberries, walnuts and rosemary; pour over inverted pie.
Broil 6 in. from the heat for 2-4 minutes or until bubbly and walnuts begin to brown. Serve warm with ice cream if desired. Yield: 8 servings.