Place the squash in a large put and cover with cold water. Bring up to a boil and simmer for about 20 minutes or until the squash is fork tender. Drain and set aside. Melt the butter in a medium saucepan and keep a close eye on it as it sizzles, foams, and eventually turns brown and smells nutty. Pour the browned butter, salt and pepper into the squash and use an immersion blender to puree until very smooth. Taste and adjust seasoning as needed.