Whisk the starches together in a large, heat-proof mixing bowl.
Bring the water to a full boil, and once boiling, turn off the heat immediately (I do this in the microwave in a glass measuring cup). Add the food colouring and stir to mix.
Working with the water right away while it's still hot, drizzle roughly 3 tablespoons of the hot water over the flour, then quickly toss with a spoon to distribute the hot water. The parts where the flour touches the water will clump up immediately. Repeat with more hot water, again 3 tablespoons at a time, until all of the flour starts to look clumpy. You should use MOST of the hot water, but you may not need all of it.
Use your hand to squeeze the flour into a ball. It should be very rough but it should come together easily. If there is still dry flour, add a little more water. If it is too wet and sticks to your hand too much, you can add a little more tapioca starch, 1 tablespoon at a time.
Once a rough dough forms, transfer it onto a clean work surface dusted with tapioca starch. Dust the top of the dough lightly with more starch and then knead until a smooth dough forms, adding more starch if the dough sticks to your hands. If there are little lumps of flour in the dough, do not worry, this will all cook away.
Separate dough into 2 pieces, and cover one with a tea towel while you work with the other. Re-dust the work surface and roll the dough out into a rectangle about 2mm thick (1/16 inch). Don’t worry too much about the dimensions.
Once you have the right thickness, cut down the sheet so you have long strips that are 2-3 inches wide. Then generously dust the strips and cut them into noodles, about 3-4 mm wide.
Toss the cut noodles with a little extra tapioca starch to ensure that they do not stick together. Repeat with the remaining dough.
Bring a large pot of water to a full rolling boil, and meanwhile prepare a large bowl of very cold water. Once the water is boiling, “sprinkle” all of the noodles into the pot. Once the noodles float, keep them boiling for another 1-2 minutes or until cooked through.
To check doneness, put a piece of noodle into the cold water; it should be translucent all the way through and it should be nice and chewy with no starchiness left in the centre. If you find it too chewy, you can cook it a bit longer.
Once done, scoop the noodles out with a wire skimmer and put them immediately into the cold water. Once cool, drain them immediately and place them into a bowl. Do not let them linger in the water unnecessarily or they will swell up.