Roasting the cauliflower adds a wonderful nutty flavor that boiling alone can’t achieve. Use an immersion blender for easier and safer pureeing. Choose good-quality bread for crispy grilled cheese croutons and cover the skillet briefly while grilling to melt the cheese evenly. Adjust bisque consistency with extra broth or almond milk if needed. The soup and grilled cheese croutons can be made ahead and reheated gently.