Preheat oven to 350°F (177°C). Spray donut pan with non-stick spray. Set aside.

Mix the brown sugar, granulated sugar, and cinnamon together in a medium bowl. Stir in the melted butter using a fork, then add the flour. Mix and crumble with a fork. Set aside.

Whisk the flour, baking powder, baking soda, salt, cinnamon, and nutmeg together in a large bowl. Set aside. Whisk the melted butter, eggs, brown sugar, milk, yogurt, and vanilla together until completely combined. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix. The batter will be very thick.

Spoon the batter into the donut cavities—I highly recommend using a large zipped-top bag for ease. Cut a corner off the bottom of the bag and pipe the batter into each donut cup, filling about halfway. Grab a handful of crumb topping and press down onto the batter of each donut. Pressing it snug into the batter helps prevent the crumb coating from falling off the donuts. (If you only have 1 donut pan, keep the remaining batter in the bowl at room temperature until you can bake the next batch.)

Bake for 10-11 minutes or until the edges and tops are lightly browned. Allow to cool for about two minutes then transfer to a wire rack set on a large piece of parchment paper. Bake the remaining donut batter and once baked, transfer to the wire rack. Dust the tops of each with a light coating of confectioners’ sugar, if desired.

Donuts are best served immediately. Leftovers keep well covered tightly at room temperature or in the refrigerator for 2 days.