Preheat the oven to 350°F (180°C). Grease a large loaf pan - one that is 9 x 5 inches (23x13cm) or 10 x 4 inches (25x10cm) in size. Line it with a parchment paper sling that sticks up a bit on each side; make sure the ends of the pan are well greased.
Cream the butter and coconut sugar with an electric mixer until fluffy. Add the egg and beat until it is well incorporated.
Mash the banana (a potato masher makes easy work of this) and add it to the batter, beating well.
Add the flour, baking powder, baking soda, cinnamon, nutmeg, and salt, and mix well. Then add the milk and vanilla and beat until it is incorporated. Add the raisins and beat on low speed to stir them in.
Scrape the batter into the prepared loaf pan and bake for 60 to 65 minutes, until a toothpick inserted in the center of the loaf comes out clean.
Allow to cool for 5 minutes in the pan, then lift the loaf up using the sling, onto a cake rack to cool completely before slicing.
Makes 1 large loaf.