Cook pasta according to package directions, adding 2 tablespoons of the salt to the water. Drain and reserve 1 1/2 cups cooking water.

Melt 2 tablespoons of the butter in a large skillet over medium-high. Add shrimp, and cook, stirring occasionally, until shrimp are pink, about 3 minutes. Add garlic, and cook, stirring often, 1 minute. Remove shrimp mixture, reserving drippings in skillet.

Add 1 cup of the reserved cooking water and remaining 2 tablespoons butter to skillet, and bring to a boil over high. Reduce heat to low; stir in Grana Padano and cracked black pepper. Cook, stirring often, until cheese melts and sauce thickens, about 1 minute.

Add cooked pasta and shrimp mixture, and toss to coat, adding remaining 1/2 cup pasta water as needed for desired consis­tency. Remove from heat; add pecorino, zest, and juice, and stir until combined. Divide evenly among 6 bowls. Sprinkle with remaining 1/2 teaspoon salt, and garnish with cracked black pepper. Serve immediately.