Wash the fennel, set aside the fronds (if any), and thinly slice the bulbs using a mandoline.
Wash the apple, core it, and slice it thinly or cut into matchsticks using a mandoline.
Place the fennel and apple in a large bowl. Add the lemon juice, olive oil, salt, and pepper, and toss everything well to combine.
Let the salad sit in the refrigerator (or a cool place) for 30 min or 2 hours. This is important to soften the fennel and allow the flavors to fully develop.
Just before serving, gently fold in the fresh mint. Divide the salad onto plates.
Carefully place the burrata cheese balls in the center. Garnish with chopped pistachios, mint leaves, and fennel fronds. Drizzle with a final touch of olive oil.
