BASIL PESTO: Heat a small nonstick skillet over medium heat. Add the pine nuts and shake the pan occasionally, until they begin to brown and give off a nutty aroma, about 2 to 3 minutes. Set aside to cool.
Combine the toasted pine nuts and basil in a food processor, pulse a few times. Add the garlic, pulse a few times more.
Slowly add the olive oil in a constant stream while the food processor is on. Stop to scrape down the sides of the food processor with a rubber spatula. Add the lemon juice and grated cheese and pulse again until blended. Add a pinch of salt and freshly ground black pepper to taste.
POTATO SALAD: Place diced potatoes into a large pot. Cover with cold water and 1 teaspoon of salt. Bring to a boil over medium-high heat, reduce heat and simmer for 5-10 minutes, until potatoes are fork tender, drain and cool.
In a large bowl, gently toss together cooled potatoes, tomatoes, mozzarella balls, pine nuts and pesto until combined. Season with salt and pepper to taste. Pour into a serving bowl and garnish with fresh basil leaves. Refrigerate until ready to serve.