Heat oven to 350°F. Generously grease 12-cup fluted tube (bundt cake) pan with shortening; lightly flour. In large bowl, beat 2 3/4 cups sugar and 1 1/2 cups butter until light and fluffy. Add vanilla and orange peel; blend well. Beat in 1 egg at a time until well blended.
In medium bowl, mix 3 cups flour, the baking powder and salt. Add to butter mixture alternately with sour cream, beating well after each addition. Gently stir in cranberries. Pour and spread batter into pan.
Bake 65 to 75 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes. Remove from pan.
Meanwhile, in small saucepan, combine 1 cup sugar and 1 tablespoon flour. Stir in half-and-half and 1/2 cup butter. Cook over medium heat, stirring constantly, until bubbly and thickened. Remove from heat; stir in rum. Serve warm sauce over cake.