Peel the skin of the cucumber and roughly chop. Remove the oil from the atsuage, then cut into bite-sized pieces.
Combine the 3 tablespoons of concentrated mentsuyu with 3x the amount in water (9 tablespoons). Add Step 1 and simmer for 15 minutes.
Coat a bowl with water and add Step 2. Chill rapidly (to blend the flavors) and cool.
Separate the liquid from boiling and the ingredients.
Place the kanten, the juices from boiling, and 1 tablespoon concentrated mentsuyu + 1 tablespoon of water (100ml total) in a pot and turn on the heat.
When it begins to boil, let it boil for 1 more minute.
Place into a small Tupperware (or plastic container) until it hardens to make the gelee.
Place the filling ingredients on a plate and top with broken up gelee right before eating. Garnish with leek.
Story Behind this Recipe
You can make this with winter melon, cucumber, or cantaloupe melon. I thought that since there is already a simmered winter melon dish, then why shouldn't cucumber be simmered too. So I tried it and it turned out delicious.
Even if you don't add the atsuage and just use cucumber, it is still delicious. Top with the very well chilled gelee right before eating. It even tastes good if the kanten isn't completely hardened.