Combine chocolate and cream in the top of a double boiler set over simmering water or in a metal bowl placed in a pan of simmering water.
Heat until the chocolate is melted, stirring constantly. (Alternatively, combine chocolate and cream in a microwave-safe bowl and microwave until melted, stirring every 30 to 45 seconds. Be careful not to let the chocolate burn.).
Pour into a warm fondue pot or into a serving bowl that can be kept warm. Add liqueur; stir gently to combine. Keep warm over low heat.