Cook spaghetti according to package directions.

While pasta cooks, chop bacon into small pieces.

In a large skillet over medium-high heat, cook bacon until crisp (5-6 minutes).

Remove bacon and drain on paper towels, reserving bacon drippings in the skillet.

Halve and slice the red onion.

Mince the garlic cloves.

Sauté onion in the reserved bacon drippings until golden brown and tender (4-5 minutes).

Add minced garlic to the skillet and sauté for 1 minute.

Add chopped collard greens to the skillet and sauté for 5 minutes.

Remove the skillet from heat and add the cooked bacon to the collard green mixture.

In a large bowl, whisk together eggs, egg yolk, kosher salt, ground black pepper, and crushed red pepper.

Add 2 1/2 cups of shredded Parmigiano-Reggiano cheese to the egg mixture and whisk to combine.

Drain the cooked pasta, reserving 1/2 cup of pasta water.

Immediately pour the hot pasta into the egg mixture and toss to coat, ensuring the heat from the pasta partially cooks the eggs.

Add the collard green and bacon mixture to the pasta and egg mixture and toss to combine.

Stir in enough reserved pasta water to reach the desired consistency.

Sprinkle the remaining 1/2 cup of cheese over the carbonara before serving.