Gluten-Free Banana Bread

Preheat the oven to 180°C (approximately 350°F). Grease a loaf pan with butter.  

Coarsely chop the walnuts. Melt the butter in a small saucepan. Mash the bananas until smooth and mix with the melted butter, sugar, vanilla sugar and egg. Sift together the buckwheat flour, baking powder and salt and stir into the banana mixture alternately with the milk. Pour the batter into the prepared loaf pan and bake for 1 hour, until a toothpick inserted comes out clean.