- 2 tablespoons vegetable oil
- 2 tablespoons unsalted butter
- 1 pound brown mushrooms, halved
- 1 teaspoon kosher salt, plus more to taste
- 1 large yellow onion, diced
- 1 tablespoon tomato paste
- 2 tablespoons all-purpose flour
- 7 cups water
- 2 tablespoons yellow miso paste
- 2 tablespoons beef base (such as Better than Bouillon®)
- 1 large bay leaf
- 1 teaspoon Worcestershire sauce
- 1 teaspoon garlic powder
- ½ teaspoon freshly ground black pepper
- ¼ teaspoon dried rosemary
- ¼ teaspoon dried thyme
- 1 pinch cayenne pepper
- 4 carrots, peeled and cut into 1-inch pieces
- 4 ribs celery, cut into 1-inch pieces
- 4 russet potatoes, peeled and quartered
- 2 tablespoons finely chopped Italian parsley (Optional)
Combine butter and vegetable oil in a pot over medium-high heat and allow butter to melt. Toss in mushrooms and season salt. Cook, stirring occasionally until mushrooms are nicely browned, 5 to 6 minutes.
Add onions and lower heat to medium. Cook, stirring, until onions have softened and are translucent and the bottom of the pot has turned brown, about 5 minutes. The browned bits on the bottom of the pot will add flavor and color. Add tomato paste and flour to thicken the stew. Cook and stir for 2 to 3 minutes.
Pour in water, increase temperature to high, and bring to a simmer. While you’re waiting for stew to come to a simmer, mix in miso paste, beef paste, bay leaf, Worcestershire sauce, garlic powder, black pepper, thyme, rosemary, and cayenne; stir to combine.
Once stew is bubbling, add carrots, and celery and reduce heat to medium-low to keep stew at a steady simmer, stirring occasionally, about 30 minutes. Taste and season with salt if necessary. Add potatoes and simmer until potatoes are very tender and creamy inside and stew has reduced and thickened, about 30 more minutes. Potatoes can be stirred in and broken up a bit to make the stew thicker.
Turn off the heat and stir in freshly chopped Italian parsley if desired.