Preheat oven to 350 degrees F.
In a large bowl, cream butter, sugar and orange zest together.
Add eggs, one at a time and beat one minute per egg.
In a separate bowl, mix dry ingredients together.
Mix buttermilk and vanilla together. Add dry ingredients alternately with the buttermilk mixture to batter. Fold in cranberries.
Grease and flour (important) 2 large bread pans.
Pour batter in pans and bake for 55-60 minutes.
Whisk glaze ingredients together until smooth. Let loaves cool before glazing.