Scrape the sides of the bowl and add one egg and stir until no trace of egg yolk remains. Add the second egg and mix again until no trace of egg yolk remains.
Add ⅓ of the flour mixture to the butter mixture and mix until just combined then add half of the sour cream mixture and mix until just combined. Add another third of the dry ingredients followed by the wet and lastly the remaining dry.
Heavily grease a 9-inch cake pan with nonstick baking spray, make sure it is a thick layer. Add the melted butter and swirl to coat the bottom of the pan and then sprinkle on the brown sugar on top.
Bake the granola cake for 35 to 40 minutes, if you gently press the top it should spring back right away or if you insert a toothpick there should be no wet batter.
Let cake cool on a rack for 5 minutes then take an offset spatula & gently run it around the sides of the cake to loosen it. Place a serving plate upside down on top of the cake and then invert the cake onto the plate to cool