Drain mandarins well on a sieve. Orange biscuits, up to 4 to decorate, crumble and sprinkle with orange liqueur. Pour the milk into a tall mixing bowl, add cream powder, whisk with the whisks of the hand mixer on lowest setting and then beat creamy for about 3 minutes on highest setting. Fold mandarins, except for 2 tablespoons for decoration, into the cream. Pour soaked cookies into dessert glasses and spread the lemon cream on top. Serve decorated with remaining biscuits, slices of mandarin orange and possibly lemon balm