Preheat oven to 180°C (350°F) using conventional oven settings (top and bottom heat). Grease a loaf pan with butter. In a separate bowl, combine flour, baking soda, and spices. Peel the bananas and mash them into a smooth puree using a fork on a plate.

Place butter, white and brown sugar in a mixing bowl and mix with a hand mixer for 3 to 5 minutes until a creamy mixture is formed.

Crack the eggs, add them to the butter and sugar mixture, and stir briefly. Then add the mashed bananas, pumpkin puree, and yogurt, and stir briefly again.

Gently stir the flour mixture into the batter in two or three stages at the slowest speed until the dry and liquid ingredients are completely combined and lump-free. Then, if desired, fold in walnuts and/or chocolate using a spatula.

Pour the batter into the prepared loaf pan, smooth the surface and bake in the oven at 180°C (top/bottom heat) for 60 to 70 minutes.

(Tip: Check the banana bread after about 50 minutes. If the surface gets too dark, you can cover it with aluminum foil.)

Remove the banana bread from the oven as soon as a toothpick inserted into the center can be pulled out without any batter sticking to it. Let the banana bread cool in the pan, then turn it out onto a cooling rack or plate and serve while still slightly warm.