Begin by preheating your oven to 350°F (175°C). Grease each cavity of a mini donut pan with cooking spray or a thin layer of butter to prevent sticking.
In a large mixing bowl, whisk together the all-purpose flour, 1/2 cup granulated sugar, baking powder, baking soda, salt, and 1/2 teaspoon of ground cinnamon until everything is well combined and free of lumps.
In a separate mixing bowl, whisk together the buttermilk, egg, and melted butter until the mixture is smooth and homogenous.
Gradually pour the wet ingredients into the bowl containing the dry ingredients. Gently fold the mixture with a spatula or wooden spoon until just combined. Take care not to overmix; a few lumps in the batter are perfectly fine.
Transfer the batter into a piping bag or a zip-top bag with a small corner cut off. Pipe the batter into each donut mold, filling each one about two-thirds full to allow space for rising during baking.
Place the filled donut pan in the preheated oven and bake for 8 to 10 minutes, or until the donuts are golden brown and spring back lightly when touched.
While the donuts are baking, prepare the cinnamon sugar coating by combining 1/4 cup granulated sugar and 1 teaspoon ground cinnamon in a small bowl. Stir well to ensure even distribution.
Once the donuts are finished baking, remove the pan from the oven and allow the donuts to cool in the pan for about one minute. After a brief cooling period, gently roll each donut in the cinnamon sugar mixture until fully coated.
Serve the donuts warm for the best flavor and texture, and enjoy your delightful treat!
Notes
For an appealing display, arrange the donuts on a decorative plate and serve with dipping sauces.