Break agar-agar into pieces and place in a kettle with the water for 1 hour to soften. Boil until agar-agar melts. Add rock sugar, reduce heat to medium, and stirring, cook until sugar dissolves. Cool 5 minutes, then stir in half-and-half and almond extract. Pour into 10 dessert bowls and chill in refrigerator. Garnish with mandarin oranges or cherries. Serves 10.