Whisk together half-and-half and 1/2 cup dulce de leche in a medium saucepan. Simmer over medium, stirring constantly, until heated through, about 10 minutes. Remove from heat, and whisk in 8 ounces chopped dark chocolate, Drambuie, vanilla, and salt until the mixture is smooth. Next, beat cold heavy cream in a cold bowl with an electric mixer on high until stiff peaks form, about 1 minute. Pour hot chocolate mixture into 4 serving cups. Top each with whipped cream, a drizzle of dulce de leche, and chopped or shaved dark chocolate. Serve with chocolate rolled wafer cookies.