Cut the butter into small cubes
Grate the butter with a box grater
Pound it gently with a rolling pin between parchment sheets
Place it in a sealed bag and submerge in warm water for a few minutes
Microwave in very short bursts at low power
Set it near a warm stove or sunny window briefly
Flatten it between two sheets of parchment with a rolling pin
Use a warm bowl or plate to cover it for faster softening