Start by cooking the pasta in salted boiling water according to the time listed on the package instructions. Add some dashi into the water for some extra flavor.
In a small bowl, assemble the sauce ingredients and whisk together until smoothly blended and the uni is relatively mixed in. Set aside.
In a skillet, begin to sauté minced onions, garlic, and red pepper flakes if using.
As the pasta is about to finish cooking, take out about a fourth cup of pasta water from the pot and reserve. Mix in pasta into the skillet. Turn the heat to low, then begin to mix in the uni carbonara sauce thoroughly, adding in pasta water if needed to adjust the consistency. Taste and season with salt and pepper if desired.
Remove from heat, top with scallions, bonito flakes, and furikake, and enjoy your delicious Uni Carbonara! This is definitely one I'm planning to make again and again.