Heat oil in a large pot over medium heat, then add the garlic and onion. Cook for 3-4 minutes or until the onions become translucent.
Add the cauliflower, followed by the broth. Place the lid on the pot and steam the cauliflower for 5 minutes or until tender.
Transfer the cauliflower mixture to a high-speed blender, followed by the soaked cashews, nutritional yeast, lemon juice, mustard, and salt and pepper to taste.
Blend until perfectly smooth, adding more liquid if needed. Taste and adjust seasoning as necessary.
Transfer the sauce back to the original pot set over medium heat and frequently stir until the sauce has fully heated.
Serve alfredo sauce over pasta or as desired.