In a heatproof bowl over hot, not simmering water, heat the chocolate till almost completely melted. Remove from the water and let stand, stirring occasionally, until the residual heat melts the chocolate completely. Let the chocolate cool until tepid. Lightly butter a baking sheet. Stir the marshmallows and peanuts into the tepid chocolate. (Stir a marshmallow into the chocolate as a temperature test. If it melts, the chocolate is still too warm; cool longer. If the chocolate stiffens, heat over hot water until the chocolate is softened.) Spread onto the prepared baking sheet. Refrigerate until firm, at least 4 hours. Cut into pieces. (Store the rocky road at room temperature in an airtight container.) Makes about 1-3/4 pounds.