Cook Onions: In a large skillet, add 3 tablespoons olive oil and add minced onion. Cook on medium, stirring constantly, until they reduce.
Cook Mushrooms: Add 8-12 ounces mushrooms and cook on medium-high, stirring constantly until they cook down (approx. 5-7 mins) and start to brown. Stir fairly constantly. Add additional olive oil, as needed to ensure pan doesn't dry out - I added a couple extra tablespoons - kind of depends how big your mushrooms are and how long they need to cook down; they will absorb the oil pretty quickly.
Season: Add 1 tablespoon fresh thyme, 1 teaspoon kosher salt and ¼ teaspoon ground black pepper; stir to combine. Add remaining 2 tablespoons olive oil and stir to coat.
Simmer: Add 5 tablespoons all purpose flour and stir to full coat the mushrooms. Add 3 cups vegetable broth, ½ cup at a time, stirring after each pour. Let simmer about 10 minutes, stirring softly, and you will see it start to thicken.
Cook Pasta: After 10 minutes, add ½ cup full-fat coconut milk and ¼ cup unsweetened almond milk. Stir to combine. Add under-cooked pasta (16 ounces fettuccine noodles) and stir to combine. Let pasta simmer in the sauce for about 5 minutes or until fully cooked, it will start to soak up the sauce.
Adjust: Taste and add any additional salt, pepper or thyme - as desired.
Serve: Enjoy immediately with additional thyme as garnish!
Notes
Noodles: feel free to use gluten-free fettuccine noodles
Re-heating: Sauce will thicken when cold. To reheat leftovers, you may want to add a splash of vegetable broth or unsweetened almond milk to help thin it out again!
Storage: Store leftovers in an airtight container in the refrigerator for up to three days.