Set a large soup pot or Dutch oven over medium-high heat. Drain the tofu, pat it dry well with paper towels, and cut it into 3/4-inch cubes if you have not already done so.

Add 1 tablespoon of the oil to the hot pot. Put the tofu cubes into the pot in one layer.

Cook the tofu for 3 to 4 minutes without moving it much, until the bottom is deep golden.

Turn the tofu with a spatula and cook for 3 minutes more, until several sides are golden. Transfer the tofu to a plate.

Add the remaining 1 tablespoon oil to the same pot. Add the sliced onion and carrots.

Cook the onion and carrots over medium heat for about 4 minutes, stirring a few times, until the onion starts to soften.

Add the lemongrass paste to the pot. Stir for 30 seconds, until it loosens into the vegetables and smells fragrant.

Pour the vegetable broth into the pot. Stir and scrape the bottom of the pot with a wooden spoon to loosen any browned bits.

Pour in the coconut milk. Stir in 2 tablespoons of the soy sauce.

Raise the heat to medium-high and bring the broth to a gentle boil.

Add the cabbage to the pot. Cook for 2 to 3 minutes, until it wilts but still keeps a little bite.

Add the rice noodles to the boiling broth. Press them down with tongs or a spoon so they are mostly covered by the liquid.