Vietnamese Shaking Beef with Lime-Pepper Dipping Sauce
Roast the sweet potatoes
Heat the oven to 400°F. Scrub or peel the sweet potatoes. Trim the ends and cut the potatoes in half lengthwise, then crosswise into ¼-inch-thick half-moons.
Grate or peel and finely chop enough ginger to measure 1 teaspoon.
On a sheet pan, toss the sweet potatoes with 1 tablespoon oil; season with salt. Spread in an even layer; roast until browned and tender, 15 to 20 minutes. Remove from the oven; toss with the ginger. While the potatoes roast, prepare the stir-fry.
Prep the stir-fry ingredients
Peel and thinly slice the red onion.
Trim the root ends from the scallions; cut the scallions into 1-inch lengths.
Finely chop, press, or grate enough garlic to measure 1 teaspoon.
Sear the steaks
Pat the steaks dry with a paper towel. Cut the steaks into 1-inch pieces; season generously with salt and pepper.
In a large frying pan over medium-high heat, warm 1 tablespoon oil until hot but not smoking. Add the steak; cook, stirring occasionally, until browned but not yet cooked through, 2 to 4 minutes. Transfer to a plate. Do not wipe out the pan. While the steaks cook, prepare the watercress and make the lime-pepper dipping sauce.
Prep the watercress and lime-pepper dipping sauce
Trim the root ends and any coarse stems from the watercress.
Juice the lime.
In a small bowl, stir together 2 tablespoons lime juice and half the salt and pepper blend; add more of the blend to taste.
Finish the stir-fry
In the same pan used for the steak, if dry, add 1 tablespoon oil; warm over medium-high heat until hot but not smoking. Add the onion, season with salt, and cook, stirring occasionally, until softened, 3 to 4 minutes. Stir in the scallions and garlic; cook until the scallions soften, 1 to 2 minutes.
Add the steak and any accumulated juices. Stir in the stir-fry seasoning base and the mirin or 2 tablespoons white wine or water; cook, stirring to coat, for 1 minute. Remove from the heat; stir in 1 tablespoon butter, if using.
Transfer the watercress to individual plates and top with the stir-fry. Serve with the sweet potatoes and lime-pepper dipping sauce.