Peel and finely dice the onions, garlic, and carrot (or grate the carrot). Wash and finely chop the parsley.
In a bowl, combine the chopped onions, garlic and carrot as well as chopped parsley, vegan ground meat, cooked brown lentils, mustard, tomato paste, and paprika, and season generously with salt and pepper. Knead the filling well with your hands so a moldable mass forms.
For each cabbage roll, carefully cut one large leaf from the white cabbage away from the stem and wash it. Cut out the lower part of the stem in the leaf with a knife. Bring salted water to a boil in a large pot and blanch the cabbage leaves in it for 4–5 minutes. Then remove the leaves from the hot water, rinse under cold water, and let them drain on a clean dish towel.
Place 2–3 tablespoons of the filling in the center of each cabbage leaf. Fold the leaves from right and left and roll the cabbage roll tightly from bottom to top so a roll forms. Secure with kitchen twine so the cabbage rolls don't fall apart. Repeat this step with all cabbage leaves until the filling is used up.
For the sauce, heat vegan butter in a large, deep pan. Fry the cabbage rolls in it so they're nicely browned on all sides. Add the tomato paste to the pan and roast it together with the cabbage rolls.
Now pour in vegetable stock until the cabbage rolls are almost covered, place a lid on the pan or roasting dish, and braise the cabbage rolls for 30 minutes over medium heat. The sauce should only simmer gently.
In the meantime, peel the waxy potatoes and place them in a pot. Cover with water, salt, and simmer for 15–20 minutes until they're soft and you can poke them with a fork.
Then remove the cabbage rolls from the pan. Mix cornstarch in 2–3 tablespoons of water and add it to the sauce. Stir in vegan cream and season the sauce with gluten-free soy sauce, marjoram, sugar, salt, and pepper to taste. Simmer for 1–2 minutes until it thickens slightly. Return the cabbage rolls to the pan and remove from heat.
For serving, wash and finely chop the parsley. Serve the cabbage rolls with the sauce and potatoes and sprinkle with parsley.