Line a 12-cup muffin tin with paper liners. Lightly grease liners with nonstick spray.
In a large mixing bowl, use a hand mixer to cream the softened ½ cup butter and 1 cup granulated sugar until smooth and creamy, about 2 minutes.
Beat in 2 eggs until combined, about 20 to 30 seconds. Add 2 teaspoons baking powder, ½ teaspoon salt, 1 teaspoon vanilla extract, and any optional spices. Mix briefly.
Add 1 cup of flour and mix until just combined. Then add ½ cup milk (or buttermilk) and stir to combine. Scrape down the sides and bottom of the bowl, then add the remaining 1 cup of flour. Mix until just combined, being careful not to overmix.
If using, use a rubber spatula to gently fold in 1 cup of any add-ins such as chocolate chips, berries, or nuts.
Divide the batter evenly among the 12 muffin cups, filling each about ¾ full. Let the batter rest while preheating the oven.
Preheat the oven to 425°F (220°C).

Bake in the preheated oven for 7 minutes. Without opening the door, reduce the heat in the oven to 350°F (175°C) and bake for an additional 13-15 minutes. Watch the muffins closely as cooking times may vary depending on your oven.
Let muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.