Preheat the oven to 425º.
Toss the cauliflower florets in the safflower oil and season with salt and pepper (a few twists of a salt and pepper grind each).
Spread the cauliflower florets out on a baking sheet and roast for 15 minutes on the middle rack. Stop and toss the cauliflower, then continue roasting for an additional 15 minutes.
While the cauliflower is roasting, heat the olive oil in a large stockpot. When shimmering, add the onion and 1 tsp salt and reduce the heat to medium-low. Allow the onions to slow cook for 20-25 minutes until the onions are dark brown.
Increase the heat to medium. Add the navy beans, vegetable broth, water and bay leaves. Bring to a low simmer. Simmer for at least 30 minutes until the beans are soft. Add the garlic and thyme and sauté for 1-2 minutes.
While the broth is simmering, prepare the vegan croutons and vegan pesto sauce. You can find the recipes here and here. When the croutons have finished baking, toss them in ½ the pesto sauce and return them to the oven for an additional 6-8 minutes. Reserve the remaining pesto sauce to garnish the soup. Allow the broth to cool slightly, then remove the bay leaves. Add the roasted cauliflower, fresh ground pepper, nutritional yeast and sherry vinegar.
Using either an immersion blender or a stand-up blender, blend the soup until creamy.
Serve the soup in individual soup bowls and garnish with a spoonful of the remaining basil pesto sauce, the basil pesto croutons, additional olive oil, salt & pepper and roasted pepitas, if desired.