Preheat the oven to 400 degrees F.

Heat the oil in a large stock pot over medium heat. Add the onions and garlic with a big pinch of salt and pepper. Add in the thyme and rosemary too. Cook until the onions soften, about 5 minutes. Add in the cauliflower and beans, along with the stock. Add another pinch of salt and pepper. Bring the mixture to a boil then reduce it to a simmer. Cover and simmer for 15 to 20 minutes, until the cauliflower is tender.

While the soup is simmering, make the croutons. Place the bread cubes on a baking sheet. Whisk together the melted butter and mustard. Drizzle over the bread, then toss very well until all the pieces are coated. Sprinkle with salt and pepper.

Roast for 10 to 12 minutes, until golden and toasty.

Carefully transfer the soup mixture to a high-powered blender. Puree until completely smooth, then pour the mixture back into the pot. Taste and season with more salt and pepper as needed. Keep over low heat until serving.

Serve the soup with fresh thyme and the mustard croutons!