1Peel and dice 1.5kg Maris Piper potatoes. Boil in salted water until tender (about 15-20 mins). Drain and mash until smooth.
2Mix in 75g butter, 3 egg yolks, and seasoning into the mashed potatoes.
3In a large pan, melt 50g butter. Add 2 finely diced shallots, 1 small sliced fennel bulb, and 2 finely sliced leeks. Cook for 5-7 minutes until softened. Season with salt and pepper.
4Sprinkle in 50g plain flour, stir for 1-2 minutes. Gradually pour in 400ml double cream, stirring to create a smooth sauce.
5Add 75g grated smoked cheese and stir until melted.