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1
Preheat oven to 325 degrees F (165 degrees C).
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2
Sprinkle both sides of flat iron steak with salt, black pepper, garlic powder, and onion powder.
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3
Heat a heavy, oven-proof skillet over medium-high heat, pour 2 teaspoons vegetable oil into the hot skillet, and heat until oil shimmers.
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4
Sear steak in the hot oil until well browned, about 3 minutes per side.
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5
Remove steak from pan and reduce heat to medium.
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6
Pour 1 more teaspoon vegetable oil into skillet; cook and stir cremini mushrooms in hot oil until wilted and browned, about 10 minutes.
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7
Lower heat to medium-low; pour wine into mushrooms and bring to a boil.
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8
Cook until wine is slightly reduced, 3 to 5 minutes; add beef stock to vegetable mixture.
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9
Bring mixture to a simmer.
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10
Stir butter and flour into a paste in a small bowl, using a fork.
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11
Stir flour paste into mushroom mixture and simmer until sauce is thickened, about 5 minutes.
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12
Place flat iron steak into skillet with mushroom sauce.
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13
Place skillet in preheated oven and cook until steak is barely pink inside, about 10 minutes.
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14
Cut steak into thin slices on the diagonal and place meat on a platter.
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15
Stir cream into mushroom sauce until heated through, 1 to 2 minutes; pour over steak and garnish with chives.
