Peel wash and chop both potato types and the celeriac into finger size chips.
Peel and finely chop the shallots.
In a nonstick deep frying pan (round-edged wok type) add the rapeseed oil. When hot, add the standard white potato chips and cook for 3-4 minutes tossing them every 1 minute. Put a lid on for the first 2 minutes and then remove. Do not add salt at this point as it will make potatoes mushy. 3-4 minutes into cooking the potatoes, add the sweet potatoes and the celeriac chips. Cook stirring/tossing regularly (ideally toss them around and do not use a metal spoon- a wooden spatula would be best if not good at tossing). Keep on turning them/tossing them every minute, minute and a half so they do not burn. Cook for about 10-12 minutes. In the last 4 minutes, add the olive oil and sprinkle all the salt you wish and cook further, allowing them to get a bit of nice and golden brown colour.
Meanwhile, but pretty much simultaneously (you are a super chef, right), place the shallots in a deeper pan or a pot (where mussels will be cooked later) with a tiny little knob of butter, salt and pepper - cook on low heat until it starts sizzling and then add half of the garlic, half of the wine and cook (increase the heat a little) for about 12 minutes or so until all wine has reduced significantly. (!!Don’t forget about tossing the potatoes in between ;-))
When the shallots are soft, add the cream cheese, double cream and creme fraiche and mix well with the cooked shallots. Lower the heat and add the mussels one by one face/flesh down. Arrange them all quickly on top of another to the last one.
Sprinkle over the remainder of the garlic, half of the parsley and pour in the remainder of the wine. Cover with a lid, shake and wobble a little the pot so the wine mixes with the creamy mix underneath and cook for about 8 minutes.
Serve the mussels on a plate (ideally face up) (1 starter portion should contain 6-8 mussels) with those beautiful home made chips and a slice of lemon. Of course you can make double the portion for a main course. Spoon some of the creamy sauce allover the mussels and enjoy along with these beautiful and so tasty homemade chips. The best in the world!