Mathilde Orange XO is a brand of [ingredient=orange-liqueur orange liqueur] made by the Gabriel & Andrieu distillery, makers of Pierre Ferrand Cognac. Mathilde Orange XO is a blend of an orange peel distillate and Ferrand Cognac, that is lightly sweetened and reduced with water to  80 proof. 

Mathilde Orange XO is substitutable for other orange liqueurs in the brandy based family: [ingredient=grand-marnier Grand Marnier] and [ingredient=mandarine-napoleon Mandarine Naopleon] are two examples. 

Mathilde Liqueur Website

Some popular cocktails containing Mathilde Orange XO