Preheat oven to 350F. Butter and flour one loaf tin and set aside. In a large bowl, mix together the bananas, sugars, butter, milk and egg. In another bowl, combine the flour, espresso powder, baking soda and salt. Pour the wet ingredients into the dry and stir until just combined. Fold in the chocolate chips & walnuts. Pour into prepared loaf pan and bake for about 55 minutes, or until the top is golden and a toothpick inserted in the middle comes out clean. Let cool in a pan for 15 minutes and then invert onto a wire rack to cool completely.