Preheat the oven to 375F and line a muffin pan with 9 paper liners.
Make the batter:
In a stand mixer bowl, cream the butter and sugar on medium speed for 5 minutes or until light and fluffy. Add the egg, vanilla, and milk, and mix until just combined.
Sift the flour, baking powder, and salt directly into the wet ingredients and mix on low speed until just combined. Add the blueberries and carefully fold them in with a rubber spatula.
Use a large spoon or cookie scoop to divide the batter into the lined muffin cups, filling each ¾th full.
Bake:
Bake for 22 minutes or until the tops are golden and a toothpick inserted in the center comes out with a few moist crumbs.
Remove from the oven, let the muffins cool down for about 10 minutes before removing them from the muffin pan onto a cooling rack.
Serve & store:
Serve these muffins slightly warm or at room temperature.
Store leftover in an airtight container on the counter for 2 days, in the fridge for up to 5 days, or in the freezer for up to 3 months.
Notes
To make the muffin batter ahead of time, scoop it into muffin tins and refrigerate overnight. In the morning, remove from the fridge while the oven is preheating.