1. Finely chop the parsley and garlic in a food processor.
2. Soften the butter in the microwave until it reaches a creamy consistency.
3. Add the butter to the parsley-garlic mixture. Season with salt and pepper. Mix.
4. Plunge the mussels into a pot of boiling water for 50 seconds to open them. Drain and return to the empty pot.
5. Add the parsley butter and mix.
6. Cover and heat over low heat for 5 minutes. Serve immediately.