Adjust oven rack to middle position and preheat oven to 375f degrees.
Spray bottom of 9 x 5-inch loaf pan with non-stick cooking spray.
In a small bowl, whisk together orange juice, orange zest, buttermilk, butter and egg. Set aside.
In a large bowl, whisk together flour, sugar, cinnamon, baking powder and baking soda.
Stir liquid ingredients into dry with until combined.
Gently stir in cranberries and nuts (if using.) Do not overmix.
Pour batter into prepared loaf pan and spread evenly. Bake for 20 minutes, then reduce heat to 350 degrees. Continue to bake until golden brown and toothpick inserted into center of loaf comes out clean, about 45 minutes longer.
Cool loaf in pan for about 10 minutes, then turn out onto wire rack and cool at least one hour before serving.
For the icing:
In a bowl, whisk together powdered sugar with one tablespoon orange juice and a teaspoon of orange zest. I prefer a thick icing but if it is too thick for your taste, just add a little more orange juice to thin it out.
Spread icing onto cooled bread. Slice and serve!
If you're using frozen cranberries, be sure to chop them while they're still frozen. Using a sharp knife to chop cranberries is important because they are thick-skinned and like to roll around on you when you chop them.