I would recommend a pretty simple approach.
Place the butter into a saucepan, and pour in enough water to cover it. Place the pan over medium heat, and allow it to become hot. Allow the butter to melt. Let it simmer for 10-15 minutes on a low heat. Pour the water/butter mixture into a ceramic or glass bowl, and allow it to cool. Place in the refrigerator until ALL butter is solid.
Poke a hole in the solid butter, and pour out the liquid water. Pour it through a colander if you must, you don't want to lose the butter in the sink!
Most of the chlorophyl, excess fertilizers, etc. will come out with the water, and your butter will be both somewhat cleaner, and better tasting!