Peel and chop potatoes into equal sized pieces, add to pan with cold water and salt
Bring to the boil and cook until soft
Drain and mash potatoes
Add 100ml cream and beat with a wooden spoon, then season
Melt olive oil and butter, then add finely sliced onions and sprouts
Soften with lid on, stirring occasionally on low heat
Remove lid, turn heat up and stir until slightly caramelised
Add caramelised vegetables to the mash and rumbledethump together
Add Dijon mustard, chives, 50ml cream and season
Melt 70g butter and add oatmeal, panko breadcrumbs, thyme, and sage leaves
Toast over medium heat until lightly golden
Add lemon zest and grated cheddar, mix to combine
Fill ovenproof dish with mash and spread to edges
Top evenly with the skirlie topping
Bake in preheated oven at 180°C (fan) for 40 minutes until golden
