This classic American salad mixes fruit, vegetables, and nuts in a light dressing.
Core and chop the apples into bite-sized pieces. Cut the lemon in half and squeeze half of it over the chopped apple, mixing them together. This will prevent the apple pieces from browning.
Add the chopped celery, grapes, and walnuts.
Mix the dressing ingredients together (yogurt, sour cream, mustard, juice from the remaining half lemon, salt and pepper), then fold it into the salad.
I prefer to use at least two types of apples. Mixing varieties provides more flavor complexity than if you use just one type of apple.
To toast the walnuts, bake them in an oven or toaster oven at 325 degrees F for 5-10 minutes, turning them a few times. For instructions on how to make candied walnuts, check out my post Stovetop Candied Walnuts.