Put the large pan of salted water to boil and cook spaghetti as per package instructions.
In the meantime, in a large shallow pan melt your butter and add peeled and bashed garlic cloves and pancetta. Fry for few minutes until garlic does its job infusing butter and pancetta is nice and crisp.
While pancetta is cooking, whisk your eggs in a bowl or a jug and add freshly grated parmesan and some freshly ground black pepper. Mix well and set aside.
When your pancetta is nice and crisp, discard the garlic and add frozen peas. Keep the pan on low heat for couple of minutes until the peas have defrosted and warmed through when you take the pan off the heat completely. If not using the peas take the pan off the heat once your pancetta is nice and crisp.
Your pasta should be ready by now and instead of draining it, use long kitchen tongs or special spaghetti serving spoon and transfer spaghetti straight from the pot it was cooking in to your pan with bacon and peas (keep that pan off the heat). You could drain your pasta in a colander if you wanted to instead but make sure to keep some of the pasta water to add to your pan with pasta, bacon and peas. It will be a base for your sauce.
Once you have transferred all your spaghetti and keeping the pan off the heat add your egg/parmesan mixture to the pasta pan and mix using wooden spatula and/or kitchen tongs making sure that pasta is nicely covered. The residual heat from the pasta will cook your egg mixture but as long as your pan is off the heat and you mix everything promptly and thoroughly, your eggs won't scramble and you will have lovely, cheesy, silky sauce.
Plate up and serve immediately with some more grated parmesan and freshly ground pepper!