Step 1In a small bowl, combine the lime juice, vinegar, sugar and water and stir to dissolve the sugar. Taste and adjust the flavors to balance the sweet and sour as needed.
Step 2Add the fish sauce, starting with 5 tablespoons and then adding more as your palate dictates, balancing the sour, sweet and salty. How much you use depends on the brand and your own taste. Aim for a light honey or amber color and a bold, forward finish. Keep in mind that this sauce is typically used to dress dishes that include unsalted ingredients such as lettuce and herbs -- ingredients that will need an extra flavor lift. When you're satisfied, add the chile. (If diners are sensitive to chile heat, serve the chiles on the side.) The sauce may be prepared early in the day and left at room temperature until serving. This makes about 1 1/2 cups dipping sauce.
Step 1To ensure the shallot slices crisp up, you must first remove some excess moisture. Using your fingers, separate the slices into individual layers, depositing them on a paper towel. Gather up the paper towel and gently blot away the moisture.
Step 2In a 10-inch skillet, heat the oil over medium-low heat. Add the sliced shallot and fry gently, stirring occasionally to ensure even cooking. After 5 to 6 minutes, when the shallot is fragrant and lightly golden, watch the progress closely, moving the slices frequently by stirring them or swirling the pan. During frying, the shallot slices will soften into a mass and then stiffen as they caramelize and crisp. When most of the slices are a rich golden brown, remove the pan from the heat. The total cooking time should be about 10 minutes. Using a slotted spoon, transfer the shallot slices to a paper towel-lined plate, spreading them out in a single layer. Discard the fragrant oil or reserve it for other uses.
Step 3When the shallot slices have cooled, crisped and darkened slightly, transfer them to a small bowl or plate. Left uncovered at room temperature, they will retain their crispiness for a good 8 hours. Even if they no longer rustle when you shake them, they are still tasty.
Step 1Marinate the beef: In a shallow bowl large enough to accommodate the beef, whisk together the cornstarch, sugar, salt, pepper, fish sauce and soy sauce until thoroughly combined. Add the beef and use chopsticks or your fingers to coat evenly. Set the mixture aside to marinate while you ready the bowls.
Step 2Make the salad mix: In a large bowl, combine the lettuce, cucumber, bean sprouts and herbs and toss well. Divide the salad among 4 noodle soup-sized bowls and top with a layer of noodles. Set the bowls aside while you stir-fry the beef.
Step 3To stir-fry a large quantity of meat successfully on a home kitchen stove, it is best to work in batches and then bring them together at the end. In a wok or large skillet, heat 1 tablespoon of the oil over medium-high heat. Add the onion and stir-fry until slightly soft and fragrant, 1 to 2 minutes. Add the garlic and stir-fry for about 15 seconds, or until aromatic. Transfer to a plate with a slotted spoon.
Step 4Increase the heat to high and add another tablespoon of oil. Add half of the marinated beef, spreading it out into a single layer. Cook the beef, undisturbed, until it begins to brown, about 1 minute, then flip and stir-fry it for an additional 1 to 2 minutes, or until it is still slightly rare. Transfer to the plate holding the onions and garlic. Repeat with the remaining 1 tablespoon oil and the second half of the beef. When the second batch is just about done, return the onion and garlic, the first batch of beef and any accumulated juices to the pan. Stir-fry for about 2 minutes to heat through and finish cooking the beef.
Step 5Remove from the heat and divide evenly among the bowls. Top with the peanuts and shallot. Serve immediately with the sauce for diners to dress and toss their own bowls.