1. Heat olive oil over medium heat in a two-quart saucepan until shimmering. Add mushrooms, kosher salt, black pepper.
2. Sauté until the mushrooms are soft and browned.
3. Add water and bring to a boil. Whisk in soup cubes until dissolved.
4. Reduce heat and simmer for five minutes, whisking often.
5. Add milk and bring to a boil over medium heat. Keep at a low boil, whisking frequently, for five minutes. The sauce will combine, thicken, and reduce slightly. If the sauce reduces a little too much, whisk in a few more tablespoons of milk. The finished sauce should just coat the back of a spoon.
6. Pour over the prepared pasta and toss to combine.