Scrub the potatoes clean. Quarter them with their skins on. Add to a pressure cooker with ½ teaspoon of salt and 1 cup of water. Cook until tender. Drain and add to a bowl. (If you don’t want to use a pressure cooker, cook in a pot.)
Roughly mash the potatoes with their skins on. You want small bits, not a smooth mash. Set aside.
Slice the cabbage into thin strips. Use a knife, mandoline or food processor for this.
Heat the olive oil over medium in a pan and add the cabbage. Season with salt and pepper. Cook covered, giving it a toss occasionally, until the cabbage wilts down–about 5-7 mins.
Wilt the spinach with the cabbage for 2 mins. Add the cabbage and spinach mixture to the mashed potatoes. Retain the pan.
To the mash and cabbage, add the flour, spring onion bottom parts (save the tops for later), and salt. Mix with your hands just enough to combine.
Form into rough patties (of about 2.5 inches). Refrigerate for at least 15 mins. Overnight is fine too.
Divide the grated cheese roughly based on the number of fritters you have. Divide the butter into small pieces.
Heat the pan over medium and add enough butter to coat the bottom of your pan in a thin layer.
Add a few fritters to the pan and cook until browned on the bottom. Flip, then add the cheese over the browned side. Cover and cook for a few mins until the cheese melts through. Cook the fritters in batches, adding more butter each time.
After the fritters are done, add the cherry tomatoes to the same pan with a little salt and olive oil. Cover and cook for 5-7 mins, squishing the tomatoes slightly to break them down. Add the spring onion tops and toss through.
To serve, place the fritters on a large plate and top with the tomatoes. Serve hot.