Chocolate filling: Boil Milk (250 milliliter), Granulated Sugar (3 tablespoon) and Agar-Agar Powder (1 teaspoon) over medium heat, then add Instant Coffee (2 teaspoon) into it and stir well. Turn off the heat and add the Semi-Sweet Chocolate Chips (100 gram) into the hot milk.
Stir the mixture till chocolate dissolves and is smooth. Then pour evenly into 8 muffin cups and place into refrigerator to set for about 15 minutes.
Remove chocolate filling jelly from cup, using a sharp knife to scrape the jelly on both sides, this will makes the jelly stick together. Set aside for later use.
Mooncake outer layer: Combine Unsweetened Cocoa Powder (2 tablespoon) and Milk (50 milliliter) together, set aside.
In a pot, combine Milk (750 milliliter), cocoa mixture, Granulated Sugar (2 tablespoon) and Agar-Agar Powder (2 1/2 teaspoon) over medium heat. Stir continuously to boil with a hand whisk.
Turn off the heat and add Nutella® (6 tablespoon) in 2-3 batches. Stir till Nutella completely dissolves and is smooth.
Pour Nutella liquid mixture into mooncake mould about 1/2 centimeter high and let it cool to semi-set about 30 seconds to 1 minute. Place the chocolate filling jelly on top.
Warm up the remaining Nutella liquid mixture and pour over the chocolate filling jelly to full.
Allow jelly to set completely and keep refrigerated until ready to serve. Enjoy!