Bring a large pot of generously salted water to a boil. Add pasta, and cook until very al dente, about 2 minutes less than called for in package instructions. Reserve 1 cup pasta water before draining.
Transfer pasta to a 12-inch skillet (preferably nonstick). Add butter and 1/2 cup pasta water. Bring to a simmer over medium-high heat. The heat helps the starch in the water meld with the fat from the butter, which prevents the Grana Padano from becoming stringy in the finished dish.
Reduce heat to low, and mix in Grana Padano and cracked pepper. Grana Padano is softer than Pecorino Romano; it will melt into the buttery water, creating a sauce as the pasta finishes cooking.
Toss pasta with tongs to thoroughly coat it with sauce. Keep everything at a gentle simmer just until cheese melts and sauce thickens slightly, about 1 minute.
Remove from heat, then stir in Pecorino Romano. (Always add Pecorino off direct heat; it clumps when cooked.) Zest lemon over the pasta. Any type of lemon will do, but a Meyer is particularly nice in this dish: It's sweeter in flavor and aroma, with back notes of orange and lime. At this time of year, you'll find Meyer lemons at specialty-food stores and some supermarkets.
If pasta looks dry, toss it with a bit more pasta water until it has a glossy coating. Divide between 2 warm bowls. Drizzle each with oil and lemon juice, and garnish with more cracked pepper. Serve immediately.