How to Make It
Prepare the Cheese Sauce: Whisk together flour and 1/2 cup milk in a bowl until smooth. Heat remaining 1 1/2 cups milk in a saucepan over medium-high until just simmering. Whisk in flour mixture, and cook, whisking constantly, until thickened, about 3 minutes. Remove from heat; whisk in cheeses, salt, and garlic powder. Cool to room temperature, about 15 minutes.
Prepare the Au Jus: Heat stock and bouillon in a small saucepan over high. Bring to a boil, and cook until reduced to 1 cup, 5 to 6 minutes. Whisk in soup mix, and boil, whisking often, until smooth, about 1 minute. Let stand 5 minutes. Strain; discarding any solids.
Prepare the Pizza: Preheat oven to 500°F; place a pizza stone in oven to preheat. Heat 1 1/2 tablespoons of the oil in a large skillet over high. Add onion; cook, stirring occasionally, until lightly browned, about 2 minutes. Lower heat to medium. Sprinkle onions with salt, and cook, stirring often, until browned and softened, 8 to 10 minutes. Remove from heat; cool slightly.
Roll dough out on a lightly floured surface into a 14-inch circle. Sprinkle cornmeal on preheated pizza stone. Place rolled dough on stone. Working quickly, spread 3/4 cup of the Cheese Sauce on dough leaving a 1-inch border. Top with roast beef, folding slices slightly to create height. Top with onions, and arrange provolone slices in a circle pattern.
Bake in preheated oven until cheese is bubbly and browned, 9 to 10 minutes. Brush edges of dough with remaining 1 tablespoon oil. Sprinkle pizza with pepper, and if desired, parsley. Cut into 8 slices, and serve with Au Jus and remaining Cheese Sauce.
Test Kitchen Tip: Ask for your meat and cheese (we used Boar’s Head brand) sliced for sandwiches at the deli counter, as this should give you just the right thickness.