1. Preheat the oven to 350ºF.
  2. Grease a 9 x 5-inch loaf pan and line it with parchment paper.
  3. Peel one banana and lay it on a cutting board. Slice it in half lengthwise to create a cut side that lays flat.
  4. In a small bowl, mash the four remaining bananas with the vanilla (you’ll have about 2 cups of mashed bananas).
  5. In a larger bowl, cream together the brown sugar, Kerrygold Unsalted Butter, then add the yogurt, and eggs, making sure no dry clumps of brown sugar remain. Add the mashed banana and stir to combine. Set aside.
  6. In a medium bowl, whisk together the flour, baking soda, baking powder, and salt.
  7. Fold this into the banana mixture, and then pour it into your prepared pan. Smooth the top with a spatula and place the sliced banana, cut side facing up, into the batter. Sprinkle with the coarse sugar.
  8. Bake for about an hour until a cake tester comes out clean, and the top of the loaf is set. Let cool in the pan for at least 20 minutes, then transfer to a wire rack to cool completely.