Prep the pans and oven. Preheat your oven to 350°F (175°C). Lightly grease your donut pans with nonstick spray or a thin layer of butter. This ensures the donuts release cleanly and the edges stay soft.

Mix the dry ingredients. In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and nutmeg. Whisking helps remove lumps and evenly distributes the leaveners.

Whisk the wet ingredients. In a separate bowl, combine buttermilk, eggs, oil, vanilla, and melted butter. Make sure the butter isn’t hot, or it may scramble the eggs.

Combine without overmixing. Pour the wet mixture into the dry ingredients. Stir gently with a spatula until just combined. Stop when you no longer see streaks of flour; a few small lumps are fine.

Fill the pans neatly. Transfer the batter to a piping bag or a zip-top bag with the corner snipped. Pipe the batter into each well, filling about 2/3 full. This gives room for rise without spilling over.

Bake until set. Bake for 9–12 minutes, rotating halfway if your oven has hot spots. The donuts are done when they spring back lightly and a toothpick comes out clean.

Cool briefly. Let the donuts cool in the pan for 5 minutes. Then turn them out onto a wire rack. This short rest helps them firm up and release easily.

Make the glaze. In a small bowl, whisk powdered sugar, 2 tablespoons milk, vanilla, and a pinch of salt until smooth. Add more milk, a few drops at a time, to reach a pourable but thick consistency.

Dip and decorate. When the donuts are just warm, dip the tops into the glaze, let excess drip off, and return to the rack. Add sprinkles or other toppings right away so they stick. For a thicker shell, double dip after the first layer sets for 2–3 minutes.

Serve fresh. These are best enjoyed within a few hours of glazing, while the edges are tender and the glaze is set.