Bring a large pot of salted water to a rolling boil over high heat. Add spaghetti and cook according to package instructions until al dente, usually about 8-10 minutes. Reserve ½ cup of the hot pasta water before draining the spaghetti in a colander.

Heat a skillet over medium heat. Add thick bacon strips and cook until crispy, about 5-7 minutes, turning occasionally. Remove excess fat, leaving about 1 tablespoon in the skillet. Stir in red chili flakes and turn off the heat.

In a mixing bowl, whisk together miso paste, whole eggs, egg yolks, and freshly grated Parmigiano Reggiano cheese until smooth. Gradually mix in the reserved hot pasta water to create a creamy sauce.

Add the drained spaghetti to the skillet containing the crispy bacon and remnants of bacon fat. Toss to coat the pasta evenly.

Off the heat, pour the miso sauce over the pasta and quickly toss until the spaghetti is liberally coated. Adjust consistency with more reserved pasta water if needed.

Plate the Miso Carbonara in warm bowls, top with additional grated Parmigiano Reggiano and freshly ground black pepper, and finish with chopped fresh parsley.