Preheat the oven to 350 degrees F (175 C).
Grease the inside of your loaf pan(with 2 teaspoons of butter or vegetable oil. Be sure to get into the corners. Add a tablespoon of sugar and shake it around to coat the bottom and sides of the pan evenly.
Sift the flour, sugar, baking soda and salt together into a bowl and whisk the ingredients together.
Microwave the butter on low power until it's barely melted. Make sure you don't boil the butter.
Add the peeled bananas, yogurt, eggs and vanilla to a blender (or you can use a bowl and stick blendeand blend until smooth. You can also mash the bananas in a bowl and use a whisk to incorporate the other ingredients.
With the blender running, pour the melted butter into the other wet ingredients and blend until smooth.
Pour the wet ingredients into the dry ingredients and fold the mixture together until it's mostly wet.
Add the chocolate and continue folding until there are no large clumps of flour. Be careful not to overmix the batter, or your banana bread will end up tough.
Dump the batter into the prepared loaf pan(and flatten off the top.
Bake for 50-60 minutes or until a skewer inserted into the center comes out more or less clean.
Transfer the banana bread to a wire rack and cool until you can handle it without mits. Remove the bread from the pan and let it cool to room temperature on the rack.