Heat up your largest dutch oven or heavy stock pot over medium-low flame. Sautee the onion (or leeks) with a drizzle of olive oil or a splash of water and pinch of salt until wilted and starts to get some color (about 10 minutes).
Add the red pepper flakes and caraways seeds then stir in the shredded cabbage. Sautee together until wilted and caramelized, making sure to stir often adding a splash of water in between If needed to help create some steam. It should be perfect in about 20 minutes. You want to get a nice caramelization all over to create flavor.
Add the diced potatoes, thyme, dill, onion powder, nutritional yeast and vegetable stock then bring to a constant simmer. Cover with a lid and cook for 25 to 30 minutes until the potatoes are cooked through and fall part. Remove from heat and discard the thyme sprigs and dill.
Use the back of a wooden spoon to mash some of the potatoes against the side of the pot. This will make your soup creamy and hearty without need to puree it at all. Taste and adjust seasonings sea salt and black pepper at this point.
Meanwhile heat up a cast iron skillet over medium high heat and pan sear the tempeh strips until golden brown on both sides.
Serve the soup garnished with fresh onion chives, red pepper flakes and crumbled with the pan seared tempeh on top.
If you prefer to add a smoky flavor to the soup you can do so by adding about 1/2 tbsp smoked paprika or a little bit of liquid smoke.