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1
Season steak with salt and pepper to taste.
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2
In a large pot, heat 1 tablespoon oil over high heat.
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3
Add steak, in two or three batches, and saute until just browned but still rare inside, about 1 minute per side, adding oil as needed between batches.
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4
Remove with a slotted spoon to a warm plate; set aside and keep warm.
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5
Decrease heat to medium, add 3 tablespoons butter to the pot and heat until melted.
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6
Add shallots and saute until they have softened, about 3 minutes.
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7
Add mushrooms and saute until they have released their liquid and are browned, about 10 minutes.
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8
Sprinkle with flour and saute for 2 minutes.
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9
Gradually whisk in stock, then Cognac; bring to a boil.
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10
Decrease heat and simmer, stirring often, until soup is slightly thickened and flavors have blended, about 15 minutes.
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11
Gradually whisk in cream and mustard; simmer for 5 minutes.
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12
Do not let boil.
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13
Meanwhile, in a large pot of boiling salted water, cook noodles until tender to the bite, 6-8 minutes.
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14
Drain, transfer to a bowl, add the remaining butter and toss to coat.
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15
Season with salt and pepper to taste; keep warm.
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16
In a bowl, whisk together the sour cream and dill.
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17
Divide beef and noodles among heated bowls and top with soup.
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18
Top each with a dollop of dilled sour cream.
