Melt butter in a saucepan over medium-low heat, adding the smashed garlic clove. Cook for about 30 seconds until fragrant.
Whisk in the flour, cooking for 2-3 minutes as the mixture bubbles to create a smooth roux.
Add milk gradually, whisking well after each addition. Bring to a gentle boil, reduce heat and whisk continuously.
Season the sauce with salt and pepper. Cook until thickened, about 5 minutes. Remove from heat.
Preheat your oven to 500°F, placing a pizza steel or stone inside for 45 minutes.
Flour a pizza peel generously and set it aside.
Flatten the dough ball on a floured surface, forming a large disk with a thick border.
Stretch the dough into a 12-inch circle and place it on the pizza peel.
Spread the garlic béchamel on the dough, leaving a 1-inch border, and top with half of the mozzarella and parmesan.
Slide the pizza onto the hot steel and bake for 5 minutes; broil for 2-4 minutes until cheese is melted.
Whisk together olive oil, balsamic vinegar, and salt in a bowl while the pizza bakes. Add arugula and toss.
Remove the pizza, let it cool slightly, top with arugula salad, slice, and serve with red chile flakes.
Repeat the process to make the second pizza.
