Add 10 cups water and 2 tsp salt to a large pot (use the same for 4 ppl). Cover and bring to a boil over high heat. While the water boils, halve the tomatoes. Thinly slice the mushrooms. Zest, then juice half the lemon (whole lemon for 4 ppl). Cut any remaining lemon into wedges. Thinly slice the chives.

Heat a large non-stick pan over medium heat. When hot, add 1 tbsp oil (dbl for 4ppl), then the mushrooms. Cook, stirring occasionally, until softened, 5-6 min. Season with salt and pepper. Transfer the cooked mushrooms to a plate and set aside.

Add rigatoni to the pot of boiling water. Cook uncovered, stirring occasionally, until tender, 10-12 min. While the pasta cooks, re-heat the same large non-stick pan over medium-high heat. When hot, add 1/2 tbsp oil (dbl for 4 ppl), then the beef and Italian seasoning. Cook, breaking up beef into smaller pieces, until no pink remains, 4-5 min.** Season with salt and pepper.

Remove the pan from the heat and add the sour cream, broth concentrate, mushrooms, lemon juice, 1/2 tsp lemon zest (dbl for 4ppl), tomatoes and half the chives. Return the large non stick pan to the stove over medium-low. Cook, stirring often until the sauce thickens slightly, 1-2 min.

When pasta is tender, reserve 1/4 cup pasta water (dbl for 4 ppl), then drain and return to the same pot. Add 2 tbsp butter (dbl for 4ppl) and the reserved pasta water to the pot with the pasta. Toss to coat.

Divide the rigatoni between bowls. Top with the beef and mushroom mixture. Sprinkle over the Parmesan cheese and remaining chives. Squeeze over a lemon wedge if desired.