• Bring a large pot of salted water to a boil. Wash and dry produce. • Halve, peel, and dice onion. Dice mushrooms into 1/4-inch pieces. Peel and mince or grate garlic. Strip rosemary leaves from stems; finely chop leaves until you have 2 tsp (4 tsp for 4 servings). Roughly chop parsley.

• Once water is boiling, add rigatoni to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. Reserve 3/4 cup pasta cooking water (11/4 cups for 4 servings), then drain.

• While pasta cooks, heat a large drizzle of oil in a large pan over medium-high heat. Add onion and mushrooms; cook, stirring occasionally, until softened, 6-7 minutes. • Add garlic, chopped rosemary, salt, and pepper; cook, stirring occasionally, until fragrant, 1-2 minutes more.

• While mushrooms cook, in a medium bowl, whisk together crushed tomatoes, flour, stock concentrates, half the vinegar, 1 cup plain water, and 3/4 tsp sugar. (For 4 servings, use all the vinegar, 2 cups water, and 11/2 tsp sugar.)

• To pan with mushrooms, add a drizzle of oil and tomato paste; cook, stirring, until tomato paste darkens, 1-2 minutes. • Add tomato-flour mixture to pan; season with salt and pepper. Bring to a boil, then reduce to a simmer. Cook, stirring occasionally, until sauce thickens, 8-10 minutes. • Stir drained rigatoni into pan with sauce, adding splashes of reserved pasta cooking water until pasta is thoroughly coated in sauce. Taste and season with salt and pepper if desired.

• Divide pasta between bowls; top each bowl with a drizzle of olive oil. Garnish with parsley and serve.