For the oatmeal cake: In a small bowl, soak the oats in the buttermilk for 1 hour. Preheat the oven to 350 degrees F; cover an 8-inch square pan with cooking spray. Mix together the flour, baking powder, salt and baking soda in a bowl. In the bowl of an electric mixer, cream the butter and sugar together at medium speed with the paddle attachment until light and fluffy, 1 to 2 minutes. Add the eggs and mix at low speed until just incorporated. Alternate adding in the flour mixture and oat mixture, beginning and ending with the flour mixture; scrape down the bowl occasionally with a rubber spatula to make sure you incorporate the flour mixture completely. Mix on low until just incorporated. Pour the batter into the square pan, making sure the batter is level in the pan. Bake until the cake is golden brown and springs back when you press it in the center, 25 to 30 minutes. Let cool for at least 30 minutes and then remove from the pan.
For the maple glaze: Put the confectioners' sugar in a small bowl. Add the maple syrup and stir with a whisk To serve: Using the whisk, drizzle the maple glaze over the cake. Slice and serve.