Peel and dice potatoes and combine with eggs, celery, and olives. In another bowl, mix together mayonnaise, pesto, and mustard. Pour dressing over salad and toss gently until well blended. Salt and pepper to taste. Arrange crumbled bacon and onion rings on top.
*Pesto: Blend together at high speed 2 packed cups fresh basil leaves, 1 to 2 large cloves garlic, 2 tablespoons grated Parmesan cheese, ½ cup olive oil. When thoroughly blended, add ¼ cup pine nuts and blend for 15 seconds more.