01 -
Melt butter in a large saucepan over medium heat. Add onion and cook 6–8 minutes until soft without browning. Stir in garlic for 1 minute.
02 -
Add cauliflower and broth. Bring to a gentle boil, cover partially and simmer 15–20 minutes until the cauliflower is very tender.
03 -
Remove from heat. Blend carefully with an immersion blender until smooth, keeping the head submerged to avoid splashes.
04 -
Stir in milk and return to low heat until steaming. Remove from heat again and add cheddar a handful at a time, stirring until melted.
05 -
Stir in mustard and pepper. If too thick, add a little water. Taste before adding optional salt because broth and cheese vary.
06 -
Serve hot with a smooth texture. Avoid boiling after adding the cheese, which can make the soup grainy.
07 -
Cool in shallow containers and refrigerate within two hours for up to three days. Reheat gently, stirring, until hot throughout.