Bring a large pot of water to a boil. Cook the wide egg noodles according to package directions until tender. Reserve 1/2 cup cooking water, then drain.

Meanwhile heat the olive oil and 1 tablespoon unsalted butter in a 12-inch skillet over medium-high heat. Add the cremini mushrooms in two batches if needed. Cook for 8 to 10 minutes, turning occasionally, until released water evaporates and the mushrooms brown. Transfer to a plate.

Reduce the heat to medium. Add the remaining 1 tablespoon unsalted butter and yellow onion. Cook for 4 to 5 minutes, until softened.

Stir in the garlic and sweet paprika for 30 seconds. Sprinkle over the all-purpose flour and stir for 1 minute, until no dry flour remains.

Gradually whisk in the low-sodium vegetable broth. Return the mushrooms to the skillet with the fine salt and black pepper. Simmer gently for 4 to 5 minutes, until the sauce lightly coats a spoon.

Turn off the heat. Whisk a few spoonfuls of the hot sauce into the full-fat sour cream in a bowl, then gently stir the mixture into the skillet. Add the fresh lemon juice. Do not return to a hard boil.

Toss in the drained wide egg noodles, adding reserved cooking water a tablespoon at a time if the sauce is too thick. Scatter with the fresh parsley and serve promptly.