Preheat oven to 350°. Cut bread into 2 inch cubes and arrange in an 9x13 pan. Combine remaining ingredients and pour over the bread. Bake at 350° for 45 minutes or until toothpick inserted comes out clean. To make the buttermilk, combine the sugar, buttermilk and butter. Once it begins to boil, remove from heat and whisk in vanilla and baking soda.