Preheat oven to 450ºF.
Melt the butter in large saucepan over medium heat. Add garlic and stir until fragrant, about a minute. Add shrimp and cook, stirring, until just opaque, about 5 minutes. Remove shrimp with a slotted spoon and keep the garlicky butter on the stove.
Place the flour in a medium bowl and whisk in about 2 tbsp the milk to make a smooth paste. Gradually whisk in the rest of the milk, then whisk the flour-milk mixture into the garlic butter on the stove. Add salt and simmer over medium heat until the sauce thickens.
Divide sauce between the prepared pizza dough rounds and top with cheese, and then shrimp. Bake until crust is golden and cheese is bubbly, 15-20 minutes, rotating pans halfway through for even browning. Sprinkle with parsley and serve.