Make this creamy mushroom and spinach pasta for an easy, healthy dinner. Be sure to save some of the pasta-cooking water as it helps the sauce emulsify.
Bring a pot of water to a boil. Cook pasta according to package directions; drain, reserving 1 cup of the cooking water. Set aside.
Heat oil in a large skillet over medium-high heat. Add mushrooms and garlic; cook, stirring occasionally, until the mushrooms are tender and beginning to brown, about 8 minutes. Whisk together half-and-half, miso and 3/4 cup of the reserved pasta cooking water in a small bowl.
Reduce heat to medium; add the half-and-half mixture to the mushroom mixture. Cook, stirring constantly, until the miso breaks down, about 1 minute. Add spinach and Parmesan; cook, stirring constantly, until the sauce slightly thickens and the spinach wilts, about 2 minutes. Add the pasta; toss gently to coat, adding more reserved cooking water if needed to reach desired consistency. Remove from heat and stir in lemon juice.