Preheat the oven to 260°C (or the highest possible temperature). Peel and quarter the onions, and slice the ginger lengthwise. Place the onion and ginger pieces on a baking sheet and roast in the oven for 5 minutes.

Meanwhile, roast the cinnamon stick, cloves and star anise in a pot over medium-high heat until the spices smell aromatic and light roasted aromas develop.

Deglaze the pot with the vegetable broth. Add the roasted onion and ginger pieces, a peeled garlic clove, soy sauce, and coriander. Simmer the broth, covered, over low heat for 40 minutes.

After 40 minutes, strain the broth through a fine sieve into a second pot . Discard any overcooked vegetables and spices, and keep the broth warm over low heat until serving.

Place rice noodles in a bowl and pour boiling water over them, then let them soak for 5 to 10 minutes according to the package instructions.

Meanwhile, heat oil in a pan, cut the tofu into thin slices, and press out excess moisture between two layers of kitchen paper. Fry the tofu slices for about 3 to 4 minutes, until the undersides are golden brown. Season the tofu with salt, turn it over, and fry for another 2 to 3 minutes on the other side.

Divide the noodles between two bowls, pour over the pho broth, and add the tofu. Top with fresh herbs and spring onions, if desired, and serve with lime wedges.