1Heat oven to 350ºF. Grease bottom and side of 12-cup fluted tube cake pan or 10-inch angel food (tube cake) pan with shortening; lightly flour. In medium bowl, mix flour, baking powder and salt; set aside.
2In large bowl, beat 1 1/2 cups brown sugar, the granulated sugar and softened butter with electric mixer on low speed 30 seconds, scraping bowl constantly. Beat on medium speed about 5 minutes, scraping bowl occasionally, until light and fluffy. Beat in eggs, one at a time, beating well after each addition. Add 2 teaspoons vanilla. Beat in flour mixture alternately with 3/4 cup milk on low speed until smooth. Pour into pan.
3Bake 1 hour to 1 hour 10 minutes or until toothpick inserted in center of cake comes out clean. Cool 10 minutes; remove from pan to cooling rack. Cool completely, about 2 hours.
4Meanwhile, in 2-quart saucepan, heat sauce ingredients except vanilla to boiling over medium heat, stirring constantly; boil and stir 2 minutes. Remove from heat; cool to room temperature. Stir in 1 teaspoon vanilla. Serve warm sauce with cake.