Stir instant coffee into chilled coffee to dissolve. Sprinkle gelatin into chilled coffee and let soften for a minute. Stir gelatin mixture into condensed milk in a small pot. Stir over low heat until gelatin dissolves. Stir in vanilla and cool to room temperature.
Whip cream to soft peaks and fold into coffee mixture in 2 additions. Spoon the mousse into serving glasses (amount of servings depends on size of glasses or cups used). Chill at least 2 hours.
Dust top of mousses with cocoa powder or cinnamon just before serving.