Set your oven to 400° F and center your oven rack.
Line a 12 cavity muffin tin with baking cups or parchment paper. If you prefer, spray with nonstick spray if you do not want to use liners.
In a large bowl, whisk together all the dry ingredients: all-purpose flour, granular sugar, baking powder, and salt. * If you are adding other spices, cinnamon or garlic, they will be added here.
In a separate small bowl, lightly beat the wet ingredients: milk, egg, and vegetable oil.* If you are adding extracts, vanilla, they will be added here.
Add the wet ingredients to the dry ingredients. Fold 18 times with a spatula.* If you are adding add-ons, fruit, chocolate chips, bacon, cheese, they will be added here. Fold batter 10 times, add the add-ons, and fold remaining 8 times.
Divide batter equally into your muffin tins, filling them 2/3 of the way full. I use an ice cream scoop to do this.
Bake for 12 – 17 minutes, this will vary based on the add-ons. The muffin should spring back to the touch when it's done and be light brown on top and sides.
Let cool for 10 minutes before removing from the muffin tin. Place on a wire rack to cool to room temperature.
At room temperature, covered, for two to three days.
In the refrigerator, covered, for one week.
In the freezer, wrapped in plastic wrap, for up to three months.