Using an electric mixer, beat the butter and sugar until smooth and creamy. Add the eggs and vanilla extract. Mix until smooth.
With the mixer on low speed, add the flour, cinnamon, baking powder, nutmeg, cardamom, salt, and milk. Mix until just combined. Do not overmix.
Fold in mashed banana and walnuts.
Preheat oven to 350 degrees F. Grease a cake pan. Pour the batter into the prepared cake pan.
Bake on the middle rack of the oven until toothpick or skewer inserted into center of cake comes out clean, about 50-60 minutes. Remove from oven and let cool in the pan for 10 minutes. Then run a thin-bladed knife around the edges to loosen.