Preheat the oven to 180°C (350°F). Lightly grease your mini donut pan.

In a medium mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt.

In another bowl, whisk the milk, egg, melted butter, and vanilla extract.

Add the wet ingredients to the dry ingredients. Stir until just combined; do not overmix.

Transfer the batter to a piping bag or zip-top bag with the corner snipped off for easier filling.

Pipe the batter into the prepared donut pan, filling each cavity about 2/3 full.

Bake for 8-10 minutes, until the mini donuts are golden and spring back when touched.

Cool donuts in the pan for 2 minutes, then transfer to a wire rack to cool completely.

For the glaze, whisk powdered sugar with milk until smooth.

Dip each cooled donut into the glaze and add sprinkles if desired. Allow glaze to set before serving.