Step 1

Heat oil in a large frying pan; cook leek and bacon, stirring, for 5 minutes or until leek softens. Remove from heat; stir in parsley.

Step 2

Layer one third of the potato in a 4.5-litre (18-cup) slow cooker; top with half the leek mixture. Repeat layering with remaining potato and leek, finishing with potato layer.

Step 3

Combine cream, milk, mustard and soup mix in a large jug, pour over potato; sprinkle with combined cheddar and parmesan. Cook, covered, on low, about 6 hours.