You will need a small cast iron pan or small oven-safe dish
Pre-heat the oven to 180C/350F fan forced.
Peel and grate the potatoes
Squeeze the liquid from the grated potato very well using a nut milk bag, cheesecloth or a clean Chux kitchen wipe. It will produce a lot of liquid so it helps to strain it in thoroughly twice - squeeze like your life depends on it. Once and then once again after letting them sit another 5 minutes.
Gently whisk the eggs with the salt and pepper. Add in the strained potato and sliced chorizo - reserve some chorizo for the top.
Grease a small cast iron pan or oven safe dish with butter or coconut oil, then pour the mixture in. Layer some chorizo on top
Cook at 180C/350F fan forced for 10-15 minutes until you can see it's mostly cooked, then cook the top with 5-10 minutes under the broiler/grill at moderate heat to cook the middle area of the top - keep an eye on it to avoid burning the top.