Preheat the oven to 170c.
Using a fork, prick the potatoes all over a few times. Place on a baking tray and put in the oven for a total of one hour, removing half-way to flip.
While the potatoes bake, make the "cheese" for the filling. Place the 350ml of plant milk, coconut oil, nutritional yeast, onion powder, garlic powder, fine sea salt, and potato starch in the cup of a high-speed blender. Blend until smooth.
Transfer to a medium saucepan and place over medium-low heat. Whisking constantly, cook until the mixture is very thick and stretchy. Remove from the heat.
Once the potatoes have baked for an hour, remove from the oven and leave to cool for 10 minutes. Hold one potato with a napkin. Working lengthways, slice off a third of each potato.
Using a spoon and working only with the sliced off 1/3, scoop out the potato to separate from the skin. Transfer all the scooped out potato to a bowl.
Using a masher or a fork, combine the scooped out potato with the vegan butter and plant milk. Mash well until smooth before adding around half of the "cheese" mixture. Mash well until fully incorporated.
Divide the cheesy mashed potato mixture between the five baked potatoes, packing the filling on top and making sure it's rough and domed rather than smoothly and flat.
Using a teaspoon, top each potato with a little of the remaining "cheese". It's best to use sparingly and I don't advise you use everything that's left in the saucepan. Top the potatoes with the black pepper and flaky sea salt (and a little knob of vegan butter if you have any spare) then return to the oven for a further 20 minutes.
After 20 minutes the potatoes should look crispy on the sides and bubbly on top. Switch the oven to grill/broil and place the potatoes nice and close to the heat element. Grill/broil the potatoes until they're golden brown and crispy on top (around 3-5 minutes) but watch them like a hawk as they'll burn easily at this stage.
Remove from the oven and sprinkle with some finely chopped parsley before serving.