Remove the veins from the prawns with heads. Cut the tomatoes and straw mushrooms in half, cut the onions into large wedges, and slice the ginger.
Combine B, and mix together. Add milk to a mug, microwave at 600W for 1 minute, and keep it in the microwave so it doesn't cool.
Add A, B, and C to a pot of boiled hot water, bring to a boil, add in the prawns, and cook through.
Add hot milk once the prawns have cooked through, and turn off the heat immediately after bringing to a boil. Decorate with cilantro and red chili pepper if available. It's also good with just thinly sliced Japanese leeks.
If you add a drop of chili oil when eating, then the red oil will float to the top, and make it even closer to Thai tom yum goong.
I've also posted a rich tom yum goong ramen made using Sapporo Ichiban ramen. Recipe ID: 2233757.
Story Behind this Recipe
I used ingredients using in Thai cooking that were close on-hand to season. Replacements as follows: lemongrass + kaffir lime leaves + galangal (Thai ginger) = ginger. Evaporated milk = hot milk. Chili oil = gochujang. It's simple and delicious, and uses ginger, so it will make even those who dislike Thai herbs happy.
Cook this quickly to avoid over boiling the ingredients. Take care especially not to over boil the prawns as they will harden. If the gochujang is soft, then add it to the pot as-is without the nam plaa. After adding hot milk, the milk will separate if you boil it for too long, so be careful.