Add 1 tablespoon vegan butter to a large, deep pan or pot over medium-high heat. Once melted and bubbling, add sliced plant-based sausage links. Cook for 10-12 minutes, stirring frequently, until browned. Remove from pan and set aside, leaving any oils released in the pan.
Turn the heat to medium and add remaining butter and olive oil. When the butter is melted, add sliced onions and a generous pinch of salt, stirring to coat. Cover and cook for about 10 minutes, or until the onions start to sizzle.
Remove the lid and cook the onions, stirring occasionally at first and more frequently as they brown, until deeply golden and caramelized, about 45 to 60 minutes. Adjust the heat as needed to maintain a gentle sizzle, and scrape any onions from the bottom to prevent burning. Once caramelized, they will be soft, sweet, and deeply golden brown.Note: Do not be tempted to rush the onions by turning up the heat! The key to caramelized onions is to go low and slow. Add minced garlic and thyme. Cook on medium-low for 2-3 minutes until fragrant, stirring frequently.
Sprinkle in flour and stir well. Cook for 1-2 minutes. This will help thicken the sauce.
Add a splash of vegetable broth and stir to fully incorporate the flour. Gradually stir in the remaining broth. Turn the heat to medium-high and bring to a boil.
Add salt and freshly ground black pepper to taste. Add pasta and stir, ensuring the pasta is just below the surface of the broth. Add an extra ½ to 1 cup of broth if necessary to fully cover the pasta.
Boil for 12 to 15 minutes, stirring occasionally, or until the pasta is al dente and the liquid has reduced and thickened. If the liquid reduces too much before the pasta has fully cooked, add just enough extra broth to cover the pasta and continue cooking until done.
Turn off the heat and stir in coconut milk, vegan parmesan, and vinegar. Add the cooked sausage back in and gently stir through.
Serve warm and top with more parmesan, chopped parsley, and toasted breadcrumbs, if desired.