For the salad: Put the chicken breasts into a large plastic storage bag. Pound with a mallet or rolling pin to flatten to 1/4-inch uniform thickness. Sprinkle the chicken with salt and pepper.
Heat a grill and drizzle with the olive oil. Grill the chicken on both sides until done, about 7 minutes per side. (Rotate halfway during grilling each side to ensure pretty grill marks.) Set aside to cool.
Grill the corn for a few minutes, until still crunchy but colored. With a very sharp knife, shave the kernels off each corn cob. Combine with the dill, celery and onions in a large bowl. Set aside.
For the dressing: Mix together the feta, half-and-half, mayonnaise and sour cream in a bowl. Stir in the sugar, lemon juice and some salt and pepper. Stir, and then taste. Add more salt if necessary; do not undersalt!
Slice the chicken on the bias to create flat, randomly shaped pieces. Throw into the bowl with the celery, onions and corn. Stir to combine. Pour half of the dressing over the ingredients and toss gently. Add more as desired, but don't overcoat the salad; it should be light! At the end, toss in the blueberries to lightly coat them in the dressing.
Spoon the salad into butter lettuce cups and then sprinkle individual helpings with feta and extra dill.