White miso in a cream sauce is an unusual combination in Western cooking and a natural one in Japanese fusion. Miso brings fermented umami depth that a standard Italian cream sauce can't match, and its salt content means you need less parmesan or added salt. The result is a cream sauce with more dimensions: creamy, savory, slightly sweet, slightly sharp.
White miso specifically is the right choice. Darker misos (red, brown, long-aged) overpower cream and turn it muddy. White miso is gentler, sweeter, and integrates cleanly into dairy without dominating it. A tablespoon and a half is enough to change the whole character of the sauce.
The shrimp comes first. Sear in butter over medium-high for 1 to 2 minutes per side until just cooked. Season simply with salt and pepper. Pull the shrimp out of the pan. The butter left behind plus the shrimp flavor in the pan is the foundation for everything else.
Scallion whites and garlic bloom briefly in the residual fat. Twenty to thirty seconds, no browning. Then the fettuccine goes directly into the pan with a cup and a half of water. This is the one-pan method: the pasta cooks in the water, absorbing the aromatic base as it softens, and the starch it releases thickens what would otherwise be a thin sauce.
Heavy cream and white miso go in once the pasta is almost tender and most of the water has reduced. Stir until the miso dissolves smoothly. Don't boil once the cream is in. Aggressive heat breaks the sauce. A gentle simmer for 30 to 60 seconds is enough to tighten everything up.
Parmesan at the end, off heat. The shrimp goes back in on top. A squeeze of fresh lime over everything pulls the whole dish into focus. Scallion greens scattered on top. The lime is the finishing touch that makes it feel balanced rather than heavy.