Bring a large pot of water to a boil with a large pinch of salt. Halve, peel, and finely chop the red onions. Mince or grate the garlic. Finely chop the tarragon reserving some for garnish. Halve the lemons. Thinly slice the mushrooms. Add the pasta to the boiling water and cook for about 10 minutes, until al dente. Be sure to reserve 1 cup pasta water.

Meanwhile, heat 2 Tablespoons olive oil in a large pan over medium heat. Add the onions and season with salt and pepper. Cook for about 5 minutes, until softened. Add the garlic and mushrooms and season with salt and pepper. Cook for about 5 minutes, until the mushrooms are golden brown.

Add the tarragon, stock concentrates, and 1 cup pasta water to the pan with the mushrooms. Cook for about 3 minutes, until slightly reduced.

Add the sour cream and stir to combine. Cook for 3 minutes until the sauce has thickened slightly. Tip: Sour cream is a great alternative to heavy cream. It has a bolder flavor and provides the same rich texture, with less fat!

Drain the pasta and add it to the pan with the sauce. Add a squeeze of lemon juice, half the parmesan, and season with salt and pepper. Toss to combine.

Serve the linguine with a sprinkle of parmesan and the remaining tarragon on top.