Prep the mushrooms. Wipe them clean and slice thickly so they keep some bite. Thin slices can get soggy.
Sweat the onions. Warm a large skillet over medium heat with 1 tbsp oil. Add onion and a pinch of salt.
Cook 5–7 minutes until soft and translucent.
Sear the mushrooms in batches. Add another tbsp oil, then half the mushrooms. Let them sit for 2–3 minutes before stirring so they brown. Cook 5–6 minutes, remove to a bowl, and repeat with the remaining mushrooms.
Add garlic and seasonings. Return all mushrooms to the pan with the onions.
Stir in garlic, thyme, paprika, and a few grinds of pepper. Cook 1 minute until fragrant.
Deglaze and build flavor. Add tamari/soy and 1/2 cup of the broth. Scrape up any browned bits from the pan.
Thicken the sauce. Whisk cornstarch into the remaining 1 cup broth until smooth.
Pour into the pan, stirring as it simmers for 2–3 minutes until slightly thickened.
Make it creamy. Lower the heat and stir in cashew cream or coconut milk along with Dijon. Simmer gently 2–3 minutes. Avoid boiling to keep it silky.
Finish and balance. Add lemon juice, taste, and adjust salt, pepper, and acidity.
The flavor should be savory with a clean, bright finish.
Serve. Spoon over noodles, rice, or potatoes. Top with parsley and an extra pinch of pepper.