Heat vegetable oil in a pot, add cinnamon stick and roasted peanuts; toast for 1 minute.
Pour in half the coconut milk and simmer until oil separates slightly.
Add diced potatoes, cardamom powder, soy sauce, sugar, salt, and water.
Simmer covered for 15 minutes until potatoes are soft.
Stir in remaining coconut milk, heat through gently, and serve warm with jasmine rice.