Step 1

Cook bacon in a skillet over medium heat until crisp, 6 to 8 minutes. Transfer to paper towels. Meanwhile, cook corn in a large pot of generously salted boiling water just until crisp-tender, about 2 minutes. Drain. When cool enough to handle, cut kernels from cobs; let cool completely.

Step 2

In a food processor, pulse scallions, garlic, anchovies, and basil until finely chopped. Add mayonnaise, sour cream, vinegar, 2 tablespoons water, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper; purée until smooth. Transfer to a large bowl. Add avocados, stirring to fully coat in dressing. Top with corn and radishes, then romaine and bacon. Cover and refrigerate up to 8 hours. Toss to combine and evenly coat in dressing (or shake vigorously, if using a bowl with a resealable lid) just before serving.