Wash and dry produce.

Trim, peel, and dice carrots into 1-inch pieces. Halve, peel, and dice onions into 1-inch pieces. Trim and quarter mushrooms (skip if your mushrooms are pre-sliced!). Dice potatoes into ½-inch pieces.

Roughly chop parsley. TIP: Place parsley in a small bowl, cover with plastic wrap, and store in the fridge until ready to use in Step 5.

In a medium microwave-safe bowl (large bowl for 8 servings), whisk together vinegar, Worcestershire, soy sauce, stock concentrates, tomato paste, garlic powder, thyme, paprika, half the flour, and 1¼ cups water (all the flour and 2½ cups water for 8) until everything is incorporated and mixture is mostly smooth (it’s OK if some lumps remain!).

Add 3 TBSP butter (6 TBSP for 8) to bowl.

Microwave for 90 seconds, then whisk for 10 seconds. Repeat microwaving and whisking twice, until butter has melted and gravy is thick enough to coat the back of a spoon. Whisk until mostly smooth, 30 seconds more.

Place beef*, carrots, onions, and mushrooms in a 5- to 6-quart slow cooker; season generously with salt and pepper. Add gravy and stir until everything is evenly coated.

Cover and cook on high until beef is tender, 3½ hours (4 hours for 8 servings).

When stew has 20 minutes left, place potatoes in a large pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes.

Reserve ¾ cup potato cooking liquid (1½ cups for 8 servings), then drain.

Return potatoes to pot along with 3 TBSP butter (6 TBSP for 8 servings); mash until smooth, adding splashes of reserved potato cooking liquid as needed.

Add half the parsley and season generously with salt; stir to combine.

Serve family style or divide mashed potatoes between bowls and top with stew. Garnish with remaining parsley.