Preheat your oven to 350°F (175°C).

In a large mixing bowl, whisk together the plain flour, sugar, ground cinnamon, baking powder, and salt until well blended.

In a separate bowl, whisk together the eggs, milk, vanilla extract, and melted butter until fully combined.

Slowly add the dry ingredients to the wet ingredients, stirring gently until the batter is smooth and well-blended.

Fill each cavity of your donut pan about two-thirds full with the batter.

Place the filled donut pan into the preheated oven and bake for 20-25 minutes.

Once baked, allow the donut pan to cool for about 5 minutes on a wire rack.

Melt some butter for coating and mix granulated sugar with ground cinnamon.

Brush each warm donut bite with melted butter and roll it in the cinnamon-sugar mixture until fully coated.

If desired, drizzle melted chocolate over half of each donut bite.