Step 1: Prepare the Dry Ingredients : In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.

Step 2: Prepare the Wet Ingredients : In a large bowl, whisk together sugar, eggs, buttermilk, melted butter, and vanilla until smooth.

Step 3: Combine Wet and Dry Mixtures : Add the dry ingredients to the wet mixture in batches, stirring until a soft dough forms. The dough should be slightly sticky but manageable.

Step 4: Roll and Cut the Donuts : Lightly flour a clean surface. Roll the dough out to about ½-inch thickness. Use a donut cutter (or a round cutter + small cap for the hole) to cut out donuts. Re-roll scraps and cut again until dough is used up.

Step 5: Heat the Oil : Pour oil into a heavy-bottomed pot or Dutch oven to a depth of about 2 inches. Heat over medium-high heat to 350°F (175°C). Use a kitchen thermometer for accuracy.

Step 6: Fry the Donuts : Fry a few donuts at a time for about 1–2 minutes per side until golden brown. Remove using a slotted spoon and drain on paper towels.

Step 7: Coat in Cinnamon Sugar : Mix cinnamon and sugar in a shallow bowl. Brush donuts lightly with melted butter (or dip one side) and immediately toss in the cinnamon sugar mixture until evenly coated.