Brown the mushrooms. Heat the oil and butter in the skillet over medium-high heat. Add the mushrooms and cook for about 7–9 minutes, stirring occasionally, until their liquid has mostly evaporated and some edges are browned. Avoid adding broth while the pan is still full of mushroom water.

Soften the aromatics. Reduce the heat to medium. Add the onion and cook for about 3–4 minutes until softened, adding a small splash of the measured broth if the pan catches. Stir in garlic, thyme, salt, and pepper for about 30 seconds.

Add the sauce base. Pour in the remaining measured broth and the cream. Scrape up the browned bits, then bring the mixture to a gentle simmer. Keep the heat below a vigorous boil so the cream does not reduce too quickly.

Cook the gnocchi. Add the uncooked shelf-stable gnocchi and stir to coat. Cover and simmer gently for about 4–6 minutes, stirring once, or until tender according to the package. Add broth a tablespoon at a time if the sauce tightens before the centers soften.

Wilt the spinach. Uncover and fold in the spinach in two additions. Cook for about 1–2 minutes until wilted. If the sauce is very loose, simmer uncovered briefly, remembering that the gnocchi will continue absorbing liquid after the heat is off.

Finish with cheese. Remove from the heat and stir in the grated cheese. Taste, then add the optional lemon juice if the sauce needs a brighter finish. Serve promptly in four shallow bowls while the sauce is still loose and creamy.