Preheat the oven to 350. Grease a 13-by-9-inch glass baking pan. Cut a piece of parchment or waxed paper to fit the bottom of the pan; put in place and lightly grease the paper.
To Make the Cake
Sift the flour, baking powder and salt together in a small bowl.
Put the sugar in a large mixing bowl and add the butter; beat on medium speed until well blended.
Add eggs one at a time, mixing well after each egg.
Add dry ingredients and milk alternately; starting and ending with the dry ingredients. Mix well.
Stir in cranberries and pour into baking pan; make sure the cranberries are evenly spaced in the batter.
Bake 30 minutes or until a wooden pick inserted in the middle of the cake comes out clean.
Let cool, remove from pan, making sure to peel off parchent paper, and arrange on a plate or stand.
To Make the Sauce
Combine all ingredients in saucepan over medium heat and cook until all the sugar and butter melts and everything has blended. Turn up heat and boil for one minute.