Garlic Mashed Potato Pizza with Arugula and Fennel Salad

Name: Garlic Mashed Potato Pizza with Arugula and Fennel Salad
Ingredients: 4 Yukon Gold potatoes, skin on, quartered; 4 cloves garlic; 4 tablespoons butter; 1/2 cup milk; Kosher salt and freshly ground black pepper; 1 tablespoon olive oil; 1 small onion, sliced; 3 anchovies, chopped; 1 sweet or spicy Italian sausage; 6-ounces prepared pizza dough; 1/2 cup grated Cheddar cheese; 2 teaspoons lemon juice; Salt and pepper; 1 cup arugula; 1/2 fennel bulb, thinly sliced; 2 celery stalks, thinly sliced; 1/4 cup shaved Parmesan cheese