Heat oven to 350°F. Grease bottom only of 8 or 9-inch square pan. Beat eggs in large bowl with electric mixer at medium speed for 2 to 3 minutes or until slightly thickened. Gradually add molasses and sugar, beating until well blended.
Add buttermilk and melted butter; mix well. Add all remaining gingerbread ingredients except chocolate chips; beat until smooth. Stir in chocolate chips. Pour into greased pan.
Bake at 350°F. until toothpick inserted in center comes out clean. For 8-inch pan, bake 43 to 53 minutes; for 9-inch pan, bake 30 to 40 minutes. Cool 20 minutes.
In small bowl, combine powdered sugar and 1/3 cup butter; beat with electric mixer at low speed until smooth and creamy. Beat in orange peel and orange juice.
To serve, cut gingerbread into squares; place on individual dessert plates. Spoon about 1 tablespoon sauce over each serving.