In a large bowl, combine water and bran. Let stand 2-3 minutes to soften; in another large bowl cream together the butter and sugar with electric mixer until fluffy. Add egg whites and vanilla to bran mixture. Beat well. Add flour, cinnamon, soda and salt. Mix well. Pour into prepared pan . Bake at 350°F for 30-35 minutes.
In a medium bowl, combine rest of ingredients for topping. Spread evenly on hot cake.
Turn on oven broiler, and broil cake near top of oven 2-3 minutes, until caramel topping is lightly browned.