Preheat the oven to 350°F (175°C). Lightly grease a mini muffin pan or line with mini paper liners.
In a large bowl, whisk together the all-purpose flour, granulated sugar, baking soda, baking powder, and salt until well combined.
In a separate medium bowl, whisk together the melted butter, milk, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. Do not overmix; the batter should be slightly lumpy.
Spoon the batter evenly into the prepared mini muffin pan, filling each cup about 3/4 full.
Bake in the preheated oven for 14 to 16 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the mini muffins from the oven and allow them to cool in the pan for 5 minutes.
Transfer the mini muffins to a wire rack to cool completely before serving.