Whip the egg yolks until light in color and thickened. Add vanilla, set aside. Melt 1-ounce pastilles in a double boiler, add cocoa powder, and coffee liqueur. Combine mixture with the yolks. In double boiler, whisk until smooth over a low flame. Whip heavy cream to stiff peaks. Fold in sugar and then fold in cream into the yolk mixture. Pour in parfait glasses.