Step 1

Preheat oven to 180C. Place potatoes in a large shallow saucepan with milk. Season well with salt and pepper. Bring to the boil and cook for 6 minutes until potatoes are tender but not falling apart. Strain into a colander over a bowl and reserve the milk.

Step 2

In a large frypan, melt 30g butter. Add onions and mushrooms and cook for 6 minutes until soft. Season well with salt and pepper. Remove to a bowl. Add remaining butter to frypan and cook garlic over gentle heat for 1 minute. Add Worcestershire sauce and allow to bubble up and reduce for 1 minute. Pour in cream and 1/2 cup of reserved milk. Remove from heat and whisk in mustard.

Step 3

Layer a third of the potatoes in the base of a large oven proof dish. Spoon over half the mushroom mixture and pour over a third of the cream mixture. Repeat with a third of the potatoes, remaining mushroom mixture and another third of the cream mixture. Finish with a final layer of potatoes then pour over the remaining cream mixture.

Step 4

Bake for 30 minutes until golden and bubbly.