Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer until the mixture is light and fluffy.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix.
Scoop tablespoon-sized amounts of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10 minutes or until the edges are lightly golden. The centers may look soft; they will firm up as they cool.
Remove the cookies from the oven and let them cool on the baking sheet for 5 minutes before transferring them to a cooling rack.
If desired, prepare the icing by mixing the powdered sugar and milk in a small bowl until smooth. Drizzle or spread over cooled cookies, and top with colorful sprinkles if desired.