1. Preheat oven to 350 degrees and grease a 9-inch springform pan. 
  2. In a medium bowl combine flour and baking powder and whisk until combined. 
  3. In a small bowl, combine melted Kerrygold salted butter, yogurt, vanilla and sugar and whisk until light and fluffy. Add eggs and whisk to combine. Pour egg mixture into flour mixture and stir until just combined. Refrigerate batter for 10 minutes. 
  4. Pour batter into prepared pan and top with sliced rhubarb. Sprinkle with sugar and bake in preheated oven for 45 minutes or until toothpick comes out clean. 
  5. Remove from oven and set on cooling rack. Let sit in pan for 10 minutes and then remove from pan and cool on wire rack. Slice and serve with whipped cream or ice cream if desired.