Prepare the Sauce Base: In a medium mixing bowl, whisk together the 4 egg yolks, 1 whole egg, the grated Pecorino Romano, and the freshly ground black pepper. Whisk until it's smooth and pale yellow. Set this aside.

Cook the Pancetta: Place the diced pancetta in a large, cold frying pan or skillet. Turn the heat to medium and cook gently for 6-8 minutes, allowing the fat to render out slowly. Once the pancetta is crisp and golden, remove it with a slotted spoon and set it on a plate, leaving the rendered fat in the pan.

Cook the Chicken: Add the olive oil to the fat in the pan. Season the chicken pieces with a pinch of salt and pepper. Increase the heat to medium-high and add the chicken to the pan in a single layer. Cook for 5-7 minutes, turning occasionally, until golden brown and cooked through. Add the crushed garlic cloves for the last minute of cooking to infuse the oil, then discard them. Return the cooked pancetta to the pan and reduce the heat to low to keep warm.

Boil the Pasta: While the chicken cooks, bring a large pot of heavily salted water to a rolling boil. Add the spaghetti and cook according to package directions until al dente (usually around 8-10 minutes). Just before draining, scoop out and reserve about 250ml (a mugful) of the starchy pasta water.

Temper the Egg Mixture: This is the most important step. Take the pan with the chicken and pancetta completely off the heat. Slowly whisk about 60ml (a quarter of a cup) of the hot pasta water into your egg and cheese mixture. What works best for me is adding it a tablespoon at a time while whisking constantly. This gently raises the temperature of the eggs without cooking them.

Combine Everything: Drain the pasta and immediately add it to the pan with the chicken and pancetta (still off the heat). Pour over the tempered egg mixture. Use tongs to toss everything together vigorously and continuously for 1-2 minutes. The residual heat from the pasta will cook the eggs and melt the cheese, creating a glossy, creamy sauce.

Adjust and Serve: If the sauce seems too thick, add another splash of the reserved pasta water, a little at a time, until it reaches your desired consistency. The final sauce should coat the pasta beautifully, not be watery or clumpy. Serve immediately in warm bowls, topped with a generous sprinkle of extra Pecorino Romano and another grind of black pepper.