brown sugar in the pan with the butter. place in the middle rack of the oven while preparing the cake batter.
-in the large mixing bowl or in the bowl of a stand mixer, place the 2/3 cups unsalted butter and cream it until light and fluffy.
-gradually add sugar and keep beating until well combined.
-add the vanilla to the eggs.
-add the eggs into the large bowl with the butter/sugar one at a time. beat until light and fluffy.
-in the medium mixing bowl, combine the sifted flour, baking powder and salt with a whisk until well combined.
-remove the pan with the butter/sugar mixture from the oven. stir the butter and brown sugar 