Bring a large pot of water to boil for the pasta. Salt the water well and add a splash of oil to prevent the pasta from sticking. When the water is boiling, add the pasta, giving it a quick stir to separate the noodles.
Meanwhile, in a heavy skillet, heat the olive oil on medium high, when the oil is hot, add the butter, and when it foams, add the garlic. Cook, stirring until the garlic is fragrant, then add mushrooms and turn the heat to high. Cook and stir until the mushrooms begin to brown, then add the sherry if using, stirring until the wine evaporates. Reduce the heat to medium and add the soy sauce, and remove from heat until the pasta is ready.
Return the skillet to medium heat and using tongs, lift the pasta from the pot, directly into the skillet, use tongs to mix the mushroom mixture into the pasta, season with salt and pepper and place on serving plates and serve.
Soy sauce adds a fermented, salty flavor, and there are low sodium varieties available.