Making the chocolate mixture: Cook the cream over medium heat until steaming. Place the chocolate into a bowl. Pour the hot cream over the chocolate and stir until everything is well combined. Add the champagne and hazelnut liqueur and mix well. Refrigerate for 2 hours to chill.
Making the truffles: After the chocolate has set, shape into truffle balls using a small ice cream scoop. Roll each truffle in the coarse sugar. Refrigerate for another 30 minutes.