- Preheat the oven to 350ºF. Grease a 9 x 9-inch baking dish and set aside.
- In a medium mixing bowl, combine 2 cups of flour, baking powder, 3/4 teaspoon of salt, and baking soda. Set aside.
- 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.
- Add the flour mixture and sour cream, alternating between the two until just combined.
- In a small bowl, combine 3/4 cup of brown sugar and 1 tablespoon of cinnamon.
- 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.
- 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.
- 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.