Heat cream in a heavy-bottomed medium-size saucepan over medium-high heat until bubbles form along edge. Lower heat to medium-low and stir in sugars, cocoa powder, butter, chocolate and salt.
Continue to heat over medium-low heat, stirring constantly, for about 10 minutes or until smooth. Remove from the heat and stir in the creme de menthe and vanilla. Allow to cool. Pour into jars. Store in airtight jars in refrigerator for up to 2 weeks. To serve, reheat gently. Makes 4 cups (12 servings).