Preheat oven to 350 degrees F.
Prepare an 8" round pan or 9" round pan by spraying lightly with non-stick cooking spray.
Using an electric mixer, mix softened butter until light and fluffy. Add in brown sugar and mix well. Add in eggs, one at a time, mixing well to combine. Add in vanilla and mix well.
Combine dry ingredients in a separate bowl. Slowly add the dry ingredients to the wet ingredients, mixing until just combined. Do not over mix. Spoon mixture into prepared baking pan.
Bake for approximately 18-23 minutes. Remove from oven and allow pan to cool on a wire rack. Once cooled, you can remove entire cookie from the pan, or slice from the pan and serve like a pie.
We love this served warm, topped with ice cream and a pinch of sea salt. You can reheat slices in the microwave for approximately 10-20 seconds.