Place chocolate chips and melted butter in a large saucepan. Heat over low heat, stirring constantly until melted.
Let cool for about 5 minutes. If the mixture is too warm, it will melt the marshmallows.
Place two large pieces of wax paper on the counter. Sprinkle about 1/4 of the coconut onto each piece (saving half the coconut) in about a 4 by 12-inch section.
Place the marshmallows and walnuts in a large bowl.
Pour the cooled chocolate mixture into the bowl and stir to mix evenly.
Transfer half the mixture onto each piece of wax paper placing it on top of the coconut. Shape into 2 logs. Sprinkle the remaining coconut on top of the logs and onto any bare sections.
Tightly wrap the logs in the wax paper and refrigerate for at least 2 hours or overnight.
Use a knife to cut the logs into slices.