Preheat the oven to 350F degrees and spray a 6-cavity doughnut pan with non-stick cooking spray. You'll end up with about 6-8 doughnuts total, so you may need to make them in 2 batches or spray 2 doughnut pans (if you have multiple).
In a large bowl whisk together the flour, cinnamon, nutmeg, cloves, baking soda and salt until combined (about 30 seconds).
To brown the butter, melt the butter over medium heat in a small saucepan over the stove. Once the butter has melted begin whisking it gently until it starts to bubble and make popping noises. After a few minutes you'll notice small brown flecks begin to form and you'll smell an almost nutty aroma. Once the butter looks almost amber in color, remove it from the stove top and let cool. After browning the butter, it will be less than ¼ cup in volume. Measure out 2 and ½ tablespoons of the brown butter (you can discard any excess).
In a medium sized bowl, gently whisk together the 2 and ½ tablespoons of browned butter with the packed brown sugar, vanilla, and maple syrup. Then whisk in the egg, followed by the sour cream and buttermilk. Add the wet ingredients into the bowl with the flour mixture, and fold everything together using a large wooden spoon or rubber spatula until combined and no lumps remain. Be careful not to overmix the batter.
Spoon the batter into the prepared doughnut pan. Alternatively, you can spoon the batter into a large ziploc bag, then cut off one of the bottom corners and pipe the batter into the doughnut pan. Fill each doughnut cavity about ½ to ⅔ full. You should end up with about 6-8 doughnuts total. Bake in the preheated oven for about 8-10 minutes or until the doughnut springs back slightly if you gently tough it with your fingers. Allow to cool in the pan for about 5 minutes before removing the doughnuts from their pan and cooling on a wire rack.