Let unsalted butter soften at room temperature until pliable
Cut the butter into small pieces
Place the butter in a mixing bowl
Beat the butter with a hand mixer or stand mixer on medium-high speed
Scrape down the sides of the bowl as needed
Continue whipping until the butter becomes light and fluffy
Add a small amount of salt if desired
Add a little milk, cream, or powdered sugar if desired for extra softness
Mix briefly until fully combined
Transfer the whipped butter to a container
Store covered in the refrigerator