French Onion Pasta is French onion soup meets spaghetti carbonara. It's creamy, cheesy, and packed with sweet caramelized onion flavor.
Bring a large pot of water to a rolling boil. Season to taste with salt. It should be as salty as sea water.
Add the butter to a large skillet. Turn the heat on medium-low. When the butter melts, add the onions, sugar, and 1/2 teaspoons salt. Toss the onions in the butter. Cook for 4-5 minutes until the onions begin to soften. Once they're soft, turn the heat down to low. Continue to cook the onions until they are very soft and a deep golden brown color. Stir every 4-5 minutes. It should take 20-25 minutes.
While the onions cook, whisk the egg yolks, parmesan cheese, cream, black pepper and remaining 1/2 teaspoon salt in a medium bowl. Set aside.
When the onions are done caramelizing, add the thyme. Cook for 1-2 minutes. Add the cognac and turn the heat up to medium. Simmer the onions and cognac until it's reduced by half. Turn the heat off and set aside.
When you add the cognac, drop the bucatini into the pasta water. Cook until just under aldente. When the pasta is aldente, use tongs to transfer the pasta to the onions. Reserve the pasta water.
Turn the heat back on a medium-low heat. Toss the pasta with the onions. Season with salt and pepper. Toss again.
Slowly whisk in 1/2 cup of the pasta water to the egg yolk and parmesan mixture. Add the mixture to the pasta and onions. Use the tongs to contiunously toss the pasta with the sauce until the pasta is hot and the cheese has melted. Keep the heat on medium-low and stir constantly. If you don't do this, you risk scrambling the eggs. Remove from heat and season to taste with salt and pepper. Garnish with thyme and parmesan cheese.