Heat oven to 375 degrees F. Coat a 10-inch pie plate with nonstick cooking spray. Whisk together flour, baking powder, salt and baking soda; set aside.
Beat granulated sugar and butter together on medium-high speed until blended. Beat in egg. On low speed, alternately beat in flour mixture and buttermilk, ending with flour mixture. Stir in raisins and caraway seeds.
Pour mixture into prepared pie plate and smooth top. Bake at 375 degrees F for 30 minutes, then reduce heat to 325 degrees F and bake an additional 15 minutes or until golden brown and toothpick inserted in center comes out clean. Remove plate to a wire rack to cool completely.
In a small saucepan, melt butter over medium heat. Remove from heat and stir in confectioners' sugar and vanilla. Add 2 tablespoons warm water and stir until mixture is thick and well blended. Spread over cooled bread and cut into wedges.