Step 1

If desired to tenderize the steak, toss steak strips and baking soda together in a medium bowl; let stand for 30 minutes. Rinse well and pat dry.

Step 2

Heat 1 tablespoon oil in a large skillet over high heat. Add half of the beef and quickly spread in an even layer. Let cook, undisturbed, until browned on the bottom, about 30 seconds. Quickly flip and cook until browned on the other side, about 30 seconds. Transfer to a plate. Repeat with the remaining beef. Do not wipe the pan clean. Reduce heat to medium.

Step 3

Add onion and the remaining 2 tablespoons oil to the pan. Cook, stirring occasionally, until the onion is starting to soften, about 2 minutes. Add mushrooms; cook, stirring occasionally, until browned and tender, about 8 minutes. Add garlic; cook, stirring constantly, until fragrant, about 30 seconds. Add noodles and stir to coat. Stir in broth, mustard, pepper and salt; bring to a boil over medium-high heat. Reduce heat to medium; simmer, stirring often, until the noodles are tender, 7 to 8 minutes, adding the beef during the last 2 minutes of cook time.

Step 4

Gently fold in sour cream until fully incorporated; simmer over medium-low heat until heated through, about 1 minute. Sprinkle evenly with parsley and chives.