Preheat oven to 350 F
In a large mixing bowl, combine softened butter and sugar
Add in mashed banana, eggs, yogurt and vanilla and stir until just combined
Add in flour, baking soda and salt and stir until just combined - do not over stir
Fold in cranberries and nuts
Pour batter into a greased 5x9 loaf pan
Bake for 50-55 minutes, or until toothpick inserted in middle of bread comes out clean