Rice Noodles with Prawns (pancit Palabok)

To make the sauce, preheat the oven to 220°C. Place the reserved prawn heads and shells on a baking tray and roast for 10 minutes.
Meanwhile, soak the noodles in cold water for 5 minutes, then cook in boiling water for 5 minutes.
Drain, refresh under cold running water and set aside.
Heat 1 tbsp of the oil in a small heavy-based saucepan over high heat. Add the celery, carrot and half each of the garlic and onion, and sauté for 5–6 minutes, or until translucent. Add the roasted prawn heads and shells, lightly crushing them to release extra flavour. Add the water and simmer for 20 minutes. Add the annatto seeds and simmer for another 10 minutes.
Strain the stock, discarding solids, into a clean pan over medium heat. Whisk in the cornstarch mixture and simmer for 1 minute, or until slightly thickened. Remove from the heat.
To make the tsitsaron crumbs, place the tsitsaron in a food processor or blender and process until it resembles coarse breadcrumbs. Transfer to a bowl, then repeat with the smoked mullet.
Heat the oil in a frying pan over high heat. Cook the garlic and onion for 5–6 minutes, or until soft and translucent, then add the crumbed tsitsaron and mullet. Reduce heat to medium and stir for 5 minutes. Transfer to a small bowl and set aside to cool.
Heat a wok over high heat until hot, then add the remaining 1 tbsp of oil. When very hot, add the squid and prawns and toss until just opaque. Add the mussels and cook for another 30 seconds.
Remove from the wok and set aside.
Add the blanched noodles and 60 ml (¼ cup) of the sauce to the hot wok and toss until heated through and well combined. Stir in half of the tsitsaron mixture, then transfer to a large plate and sprinkle over remaining tsitsaron mixture. Top with seafood, eggs and spring onions. Spoon over a little more sauce and serve with calamansi.