Whisk together the sour cream, mayonnaise, lime juice, cilantro, kosher salt, and cracked black pepper in a medium bowl until smooth and well combined. Set aside about 3/4 cup of this dressing for the corn mixture, leaving roughly 3/4 cup in the bowl for final plating. This creamy lime-cilantro base is the foundation for the entire salad's flavor profile.
Heat the olive oil in a large skillet over medium heat and sauté the diced jalapeño for 1-2 minutes until fragrant. Increase the heat to medium-high, add the corn kernels and granulated sugar, then cook for 4-5 minutes, stirring occasionally, until the corn develops some golden-brown color and develops deeper, charred flavor. I like to listen for a gentle popping sound in the pan—that's when you know the corn is caramelizing properly. Transfer the cooked corn to a bowl and let it cool for about 10 minutes.
Once the corn has cooled slightly, add most of the reserved dressing from Step 1 (about 3/4 cup), the crumbled queso fresco, and 2 1/2 teaspoons of chili powder to the corn mixture. Fold gently to combine, allowing the flavors to meld. The warm corn will absorb the creamy, tangy dressing beautifully. Set this aside while you prepare the shrimp.
Pat the shrimp dry with paper towels—this is crucial for achieving a good sear. In a small bowl, combine the chili powder, smoked paprika, onion powder, garlic powder, and ground cumin. Toss the shrimp with just enough olive oil to coat lightly, then dust generously with the spice mixture. Heat a large skillet over high heat until it's very hot, then add the shrimp in a single layer and cook for 2-3 minutes per side until they turn pink and opaque. I always finish the shrimp with a squeeze of fresh lime juice right in the pan—it adds brightness and prevents the spices from tasting too heavy. Transfer to a plate.
Divide the chopped romaine lettuce among serving plates or bowls as your base. Arrange the seared shrimp from Step 4, the corn salad from Step 3, sliced avocados, radishes, and extra queso fresco on top of the lettuce. Thin the remaining dressing from Step 1 with 2-3 tablespoons of milk to reach your desired consistency, then drizzle generously over each salad. Garnish with extra fresh cilantro and a light dusting of chili powder. Serve immediately with lime wedges on the side for guests to adjust the citrus level to their preference.