1. Sauté onion in butter and oil with a pinch of salt until soft, 4–5 minutes. Add garlic; cook 30 seconds.

2. Add broccoli, potato, and broth; simmer until tender, 12–15 minutes.

3. Blend until mostly smooth, leaving some texture. Stir in milk, cheddar, and mustard powder; warm gently until melted (do not boil).

4. Season with salt and plenty of black pepper. Garnish with chives.