In a large pot of boiling salted water, cook pasta according to package instructions; drain well.

Melt butter in a large skillet over medium high heat. Add mushrooms and shallots, and cook, stirring occasionally, until mushrooms are tender and browned, about 5-7 minutes; season with salt and pepper, to taste.

Stir in garlic and thyme until fragrant, about 1 minute.

Whisk in flour until lightly browned, about 1 minute.

Gradually whisk in beef stock and Dijon. Bring to a boil; reduce heat and simmer, stirring occasionally, until reduced and slightly thickened, about 4-5 minutes.

Stir in pasta and sour cream until heated through, about 1-2 minutes. Stir in Parmesan until melted, about 1 minute. Stir in parsley; season with salt and pepper, to taste.

Serve immediately.