Bring a large pot of water to a rolling boil (do not salt the water). Set a medium or large bowl of ice water nearby. Cook the corn for 3 minutes, then use tongs to transfer the corn to the ice water to halt the cooking process. (Note: if you're using very fresh corn from the farmer's market, you may be able to skip this step use the corn raw! Slice off a few of the kernels and taste them).
Once the corn has cooled, slice the kernels off the cob and place in a large bowl. Add the shallots, tomatoes, basil, and feta.
In a smaller bowl, whisk together the vinegar, olive oil, salt and pepper. Drizzle 1/2 to 3/4 of the dressing into the salad, gently tossing the ingredients together. Add the remaining vinaigrette if desired. Taste and add additional salt and pepper if needed.
Serve at room temperature or chilled. The salad will keep for several days in the refrigerator in an airtight container or covered tightly with plastic film, but it will begin losing its texture and flavor after 48 hours.
If you’re using fresh corn, keep in mind that it varies in size; don’t worry about a specific number of cups. Just know that using more or less corn may slightly impact the amount of salt and pepper you need to use, which is why I suggest seasoning to taste.