Bring a large pot of generously salted water to a boil. Cook the pasta until al dente according to the package directions. Reserve 1/2 cup of pasta water, then drain.

Heat the olive oil and butter in a large skillet over medium-high heat. Add the sliced mushrooms in an even layer and let them cook undisturbed for 3 to 4 minutes.

Stir the mushrooms and continue cooking for 4 to 5 minutes, until deeply browned and their released moisture has evaporated.

Reduce the heat to medium. Add the shallots and cook for 2 to 3 minutes, until softened. Stir in the garlic and cook for 30 seconds, until fragrant.

Add the white miso paste and a small splash of reserved pasta water. Stir until the miso has dissolved into a smooth mixture.

Pour in the heavy cream and bring the sauce to a gentle simmer. Cook for 2 to 3 minutes, stirring occasionally.

Add the grated Parmesan and black pepper. Stir until the cheese has melted and the sauce is smooth. Taste before adding any extra salt.

Add the drained pasta to the skillet. Toss well, adding reserved pasta water a little at a time until the sauce is glossy and coats every strand.

Divide among bowls and garnish with chopped parsley, extra Parmesan, black pepper, and toasted sesame seeds if desired. Serve immediately.