Bring 6 quarts of water to a boil and add 2 tablespoons salt. In a 12-inch saute pan, cook the onion and guanciale over medium heat until both the onion and the guanciale are translucent, 8 to 10 minutes.
Add the spaghetti to the boiling water and cook according to package instructions, until tender but still al dente, and drain well. Add the hot pasta to the saute pan and toss over medium heat until coated. Add 1/4 cup of the cheese and stir through. Remove from the heat and vigorously stir in the egg whites.
Divide the pasta among 4 plates and top each serving with 1 yolk. Sprinkle with the remaining 1/4 cup grated cheese and the black pepper. Serve immediately.
Note: "Raw eggs should not be used in food prepared for pregnant women, babies, young children, the elderly, or anyone whose health is compromised."
*RAW EGG WARNING
Food Network Kitchens suggest caution in consuming raw and lightly-cooked eggs due to the slight risk of Salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly-refrigerated, clean, grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.
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