Preheat the oven to 350º F. Grease and flour a 9-inch loaf pan. Mix the dry ingredients from the flour to the spices in a large bowl. Combine eggs, buttermilk, and butter in a medium bowl. Make a well in the dry bowl and add the wet. Stir until just moist. Fold in the blueberries and the nuts. Spoon into the pan and bake for 60 minutes to 75 minutes. Cool in the pan on a rack. Wrap and store overnight.
Drizzle with the icing the next day. To make the icing, melt the chocolate, stir in the sugar, and then add milk tablespoon by tablespoon until it's thin enough to drizzle. Chill the loaf in order to set.