Green Beans with Mushrooms

Bahan-bahan (6 porsi)

• 1 1/2 pounds fresh green beans (trimmed)
• 1 teaspoon Diamond Crystal kosher salt (plus more as needed)
• 1/4 teaspoon fresh black pepper
• 8 ounces cremini mushrooms (cut into thick slices)
• 1 small red onion (halved and thinly sliced (I also tested with a shallot and both are good))
• 1 1/2 tablespoons unsalted butter (cut into a few pieces)
• 3/4 cup low-sodium chicken stock (plus more as needed)