Prepare the Bread: Preheat oven to 350°F. Grease a 9-inch loaf pan with butter, and set aside. Combine flour, cinnamon, nutmeg, ginger, baking powder, cloves, and 1/2 teaspoon salt in a large bowl. Whisk together brown sugar, sweet potato, oil, and 1 teaspoon vanilla in a separate bowl until well blended. Add eggs, 1 at a time, to brown sugar mixture, whisking to combine after each addition. Slowly add brown sugar mixture to flour mixture, whisking constantly until well combined.
Transfer batter to prepared loaf pan. Bake on middle rack in preheated oven until a wooden pick inserted in center comes out clean, about 1 hour. Remove bread from oven; cool in pan on a wire rack 15 minutes.
Prepare the Icing: Whisk together powdered sugar, buttermilk, lime juice, 1/2 teaspoon vanilla, and pinch of salt in a medium bowl until smooth.
Remove bread from pan, and cool on wire rack. Drizzle bread with icing while bread is still warm.