Peel and cut the potato into 1/2-inch pieces and place in a medium pot. Fill the pot with enough water to cover the potatoes and add a large pinch of salt. Bring to a boil and cook for 15-20 minutes, until easily pierced with a knife. Drain, return to the pot, and set aside, covered, to keep warm.

Slice the mushrooms. Halve, peel, and thinly slice half the onion. Mince or grate the garlic. Remove and discard the ribs and stems from the mustard greens, then coarsely chop the leaves.

Heat 1 tablespoon olive oil in a large pan over medium-high heat. Add the mushrooms and cook, tossing, for 6 minutes, until softened and golden brown. Season with salt and pepper. Remove from the pan and set aside.

In the same pan, heat another 1 tablespoon olive oil over medium heat. Add the onions and cook for about 5 minutes, until softened. Add the dried thyme and garlic and cook for 30 seconds, until fragrant. Add the mustard greens and cook, tossing, for about 3 minutes, until slightly wilted.

Add the stock concentrate and 1/2 cup water and cook for 5 more minutes, until greens are wilted. Add the paprika and half the sour cream and stir to combine. Simmer until thickened, about 5 more minutes. Add the mushrooms and stir to combine.

Mash the potatoes with dijon mustard, remaining sour cream, and a pinch of salt and pepper.

Serve mushroom mixture on a bed of mashed potatoes. Enjoy!