Peel and crush the garlic. Finely chop the dill leaves. Finely grate the zest off the lemon. Juice it into a fairly large bowl.
Flake the roast smoked salmon off the skin into a separate bowl. Set aside.
Trim the top and bottom off the celeriac. Slice the roots off the celeriac at an angle, so you take off most of the tangled roots but not the whole bottom. Wash and peel the celeriac.
Use a vegetable peeler to peel long, thick noodles off the celeriac. Or, use a spiraliser if you have one. Celeriac browns quickly, so add the noodles to the bowl of lemon juice and toss every so often to coat.
Bring a pan of salted water to the boil. When it has reached a rolling boil, add the celeriac and lemon juice. Simmer for 3-5 mins to just cook the noodles. Drain them well.
Warm a deep frying pan or wok over a medium heat for 1 min. Add 1 tsp oil. Fry the garlic for 30 secs. Add the celeriac noodles, most of the dill and lemon zest, the salmon and half the pot of crème fraîche.
Stir and gently heat the noodles for around 5 mins to warm through. Taste and season. Heap them into warm bowls. Garnish with the remaining dill and lemon zest. Serve with the sweet salad mix on the side.