Bring a large pot of salted water to boiling.
Meanwhile, in a large skillet over medium high heat, add the bacon and cook until brown and crispy, about 5 to 7 minutes. Reserve 2 tablespoon bacon fat and discard remainder. Add garlic and cook, stirring, 1 minute or until fragrant. Remove skillet from heat.
In a medium bowl, whisk together eggs and Parmigiano-Reggiano cheese; set aside.
Cook pasta according to package directions. Before draining, set aside 1 cup pasta water; drain pasta. Whisk ¼ cup reserved pasta water into egg mixture,
Transfer pasta to the skillet and toss with the bacon fat. Very slowly stream egg mixture in skillet, tossing constantly, about 3 to 5 minutes or until cheese is melted and egg is thickened. Season to taste with salt and pepper. Add reserved pasta water, one tablespoon at a time, until desired consistency is reached.
Serve garnished with parsley, if using.