Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente according to package timing.

While the pasta cooks, heat a pan over medium. Add the diced pancetta and cook until the fat renders and the pieces are crisp. If using garlic, add whole cloves early, then remove before the next step.

In a bowl, whisk the two egg yolks with the grated Parmesan until smooth and slightly thickened. Season lightly with black pepper.

When the pasta is nearly done, scoop out about ½ cup of the starchy cooking water and set it aside. Drain the pasta quickly, leaving it hot.

Transfer the hot pasta to the pan with the pancetta. Remove the pan from the heat immediately.

Pour the egg-and-cheese mixture over the hot pasta and stir vigorously. The residual heat will cook the yolks gently and create a glossy sauce.

If the sauce seems too thick or clumpy, add a tablespoon or two of the reserved pasta water at a time and toss until silky.

Taste and season with a pinch of salt if needed, and lots of freshly ground black pepper. Serve at once, garnished with chopped parsley if using.