Cook pasta according to packaged instructions.
Heat a large skillet over medium heat. Add vegan butter and melt.
Add onions and saute for 4-5 minutes, stirring often so not to burn and they caramelize a bit and start to turn golden brown.
Add mushrooms and salt. Saute for 5-7 minutes, stirring often until they start to soften. Add in garlic and pepper and saute for 1 minute.
Add in thyme sprigs, nutmeg, allspice, smoked paprika, and ¼ cup vegan beef broth and scrape off any bits at the bottom. Cook for another 3 minutes, stirring often.
Into a small bowl, add flour and remaining broth and whisk together. To the same bowl, add dijon and Worcestershire in and whisk again. Pour into skillet and stir together well. Reduce heat and cook for another 5 minutes on simmer.
Remove from heat. Take out and discard thyme springs. Stir in sour cream. Stir until combined. Adjust seasonings to taste, serve over cooked pasta. Add parsley for garnish if desired.