I grew up eating sweets from Hanazono Manjyu. Today, you can purchase their sweets at any major department store. Their flagship store is located across the street from the Hanazono Shrine on Meiji Dori Street just a few blocks away from the Shinjuku 3-chome crossing. They have been in the confectionary business since 1834.
They sell their products on the first floor, and on the second floor there is a hidden tea lounge.
I ordered the Anmitsu bowl, it contained Kanten seaweed jello cubes (clear ones and green tea kinds), beans, dried fruits, azuki bean paste and sugar coated mochi. You can pour brown sugar syrup over your bowl to taste. It also comes with free sweet beans that have been one of the best seller products of Hanazono Manjyu for over 60 years. After you enjoy your Annmitsu and cold tea, they will serve you a cup of hot green tea. For 945 yen, all of this seems very reasonable to me.