1. Preheat the oven to 350ºF. Grease a 9 x 9-inch baking dish and set aside.
  2. In a medium mixing bowl, combine 2 cups of flour, baking powder, 3/4 teaspoon of salt, and baking soda. Set aside.
  3. In a large mixing bowl, cream the softened Kerrygold Unsalted Butter and granulated sugar together until light and fluffy. Add the eggs, one at a time. Add the vanilla and beat well.
  4. Add the flour mixture and sour cream, alternating between the two until just combined.
  5. In a small bowl, combine 3/4 cup of brown sugar and 1 tablespoon of cinnamon.
  6. Add half of the batter to the pan and spread evenly with a spatula. Sprinkle the brown sugar mixture on top. Dollop the remaining cake batter on the brown sugar mixture, and spread it evenly.
  7. Whisk the remaining brown sugar, the melted Kerrygold Unsalted Butter, cinnamon, and salt in a medium bowl. Add the remaining flour and mix well. Sprinkle the streusel evenly over the batter.
  8. Bake for 35-40 minutes until a cake tester inserted into the center comes out clean. Transfer to a wire cooling rack and let cool for at least 30 min before slicing and serving.