Preheat your oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or lightly grease it with non-stick spray.
In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt. Make a well in the center of the dry ingredients.
In a separate medium bowl, whisk together the whole milk, vegetable oil (or melted butter), egg, and vanilla extract until well combined.
Pour the wet ingredients into the well of the dry ingredients. Stir gently with a spoon or spatula just until moistened. Do not overmix; the batter should remain slightly lumpy.
Spoon the batter evenly into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 15 to 18 minutes, or until the muffin tops are golden and a toothpick inserted into the center comes out clean.
Remove from the oven and allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Store leftover muffins in an airtight container at room temperature for up to 3 days, or freeze for up to 3 months.