1. Cook the pasta: Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package directions until al dente.
2. Meanwhile, chop up your shallots, garlic and mushrooms.
3. While the pasta is cooking, heat the olive oil in a large skillet over medium-high heat. Add the mushrooms, shallots and garlic and cook, stirring occasionally, until golden brown & tender.
4. Build the sauce: Stir in the mushroom glace, miso paste, vinegar & soy sauce. Bring to a simmer and cook for 5 minutes, or until the sauce has thickened slightly.
5. Combine and serve: Add the spinach to the skillet and cook until wilted, about 2 minutes. Stir in the drained spaghetti and toss to coat. If the sauce is too thick, add a little of the reserved pasta water to thin it out.
6. Season to taste.
7. Garnish and enjoy: Serve immediately.