Garlic Mashed Potatoes: Combine potatoes, broth, and garlic in a large saucepan. Add additional water if necessary in order to keep all potatoes completely submerged. Bring to boil than reduce heat to low. Continue to cook until potatoes are tender, 25 to 30 minutes.
Drain and mash the potatoes and garlic. Add butter, salt, pepper, and whipping cream. Whip until it has a creamy texture.
Preheat the oven to 450 degrees F with a pizza stone.
Roll out the dough into a 1/4-inch thick circle. Place in a pizza pan or on a pizza peel. Spread on the garlic mashed potatoes. Evenly sprinkle the sauteed onions. Layer the sliced tomatoes. Evenly sprinkle the cheeses, bacon crumbles, cracked black pepper, and onion salt. Bake for 10 to 12 minutes.
Combine flour, salt, and yeast and mix well in a large bowl (12 quart will work fine). Mix in the oil and warm water. Cover the bowl and let the dough rise for 30 minutes.