Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x5-inch loaf pan.
Stir melted butter and sugar together in a bowl. Add eggs, milk, and vanilla extract and mix well.
Combine sifted einkorn flour, cinnamon, baking soda, baking powder, and salt in a separate bowl. Stir into the butter mixture until smooth. Fold walnuts and mashed bananas into the batter until well mixed. Spread batter evenly into the prepared pan.
Bake in the preheated oven until an instant-read thermometer inserted into the center of the loaf reads 195 degrees F (90 degrees C), about 55 minutes. Cool loaf in the pan for 10 minutes, then remove from the pan and transfer to a wire rack until completely cooled.