Moules-frites

How to make it

1. Peel the Bintje potatoes and cut them first into slices about 1 cm thick, then into sticks of the same thickness. Even sticks are the whole point: the thin ones will be burnt black by the time the thick ones are finally tender. Put the sticks in a bowl of plenty of cold water. ⏱ 15 min
2. Let the sticks sit in the cold water for 10 minutes, until the water turns milky from the surface starch that would otherwise make the fries stick together in the tallow. ⏱ 10 min · passive
3. Drain the water and pat the sticks completely dry in a clean kitchen towel, so there isn't a single wet surface left. Water in hot tallow will make it boil over the edge.
4. Scrub the mussels under cold running water and pull off the beard with a firm tug toward the tip of the shell. Discard any mussels with cracked shells, and tap the open ones against the edge of the counter — if they don't close within a couple of seconds, they're dead and should be thrown out. In the end, the shells should be clean and glossy black. ⏱ 15 min
5. Whisk the egg yolks, Dijon mustard, white wine vinegar and salt together in a bowl, then whisk in the neutral oil — drop by drop at first, then in a thin stream once the mixture has taken hold. The yolks should be at room temperature, since cold oil into cold yolks will split. The mayonnaise is done when it's thick, glossy and holds the trail of the whisk. Keep it cold. ⏱ 10 min
   Chef's tip The first tablespoon of oil decides it: go too fast there and it never takes. If it does split, put a fresh yolk in a clean bowl and whisk the broken mixture into it drop by drop — it comes back every time.
6. Melt the beef tallow in the deep-fryer over medium heat and heat it to 150°C, measured with a meat thermometer. The tallow should be completely clear and still on the surface, with no haze of undissolved fat. ⏱ 10 min
7. Fry the dried sticks in three batches, 6-8 minutes per batch, so the tallow doesn't drop in temperature. They should become tender all the way to the center, but still be pale and soft with no golden color. Lift each batch out with a slotted spoon and let them drain on a rack. ⏱ 20 min–25 min
   Chef's tip Each cold batch pulls the tallow down 15-20°C, so let the thermometer climb back to 150°C before the next goes in. Listen: a lively, steady bubbling means water is leaving the potato — sluggish, quiet fat means it's soaking in instead.
8. Let the parboiled sticks cool completely on the rack for 30 minutes, until they feel dry and slightly leathery on the outside. That drying-out is what gives the crisp crust on the second fry. ⏱ 30 min · passive
9. Melt the butter in the large pot over medium heat and sauté the finely chopped shallots and sliced celery for 5 minutes. They should turn soft and translucent without taking on the slightest color.
10. Pour in the white wine along with the bay leaves and thyme sprigs, and bring to a boil over high heat for 2 minutes, until the steam smells of wine and no longer sharply of alcohol.
11. Add the cleaned mussels to the pot, cover with the lid and steam over high heat for 5-7 minutes. Shake the pot a couple of times along the way, so the ones on the bottom trade places with the ones on top and finish at the same time. They're done when the shells stand wide open and the meat has drawn together and firmed up. Discard any mussels that are still closed.
    Chef's tip Take the pot off the heat the moment most shells are open — the last few finish on residual heat with a shake of the lid on. A minute too long and the meat shrinks to a tough little nub, and no broth wins that back.
12. Take the pot off the heat and fold the roughly chopped parsley into the broth. Season the broth with freshly ground black pepper and salt if needed — the mussels have already released their own salty seawater, so always taste before you salt.
    Chef's tip Ladle the broth from the top and leave the last centimetre in the pot — sand and grit from the shells settle there and will otherwise end up gritty in every plate.
13. Put the lid back on the mussels to keep them warm, and at the same time turn up the tallow to 175°C. The thermometer should sit steady at temperature before the fries go back in.
14. Deep-fry the cooled sticks in three batches for 2-4 minutes per batch, until deeply golden and rattle dry against the slotted spoon. Toss each batch in fine salt immediately, while still glistening with fat, so the salt sticks to the crust. ⏱ 6 min–10 min
    Chef's tip The fries need to hit the table within a few minutes. Steam from the hot center pushes out through the crust, and piled deep with no air around them they go limp surprisingly fast.
15. Set the pot of mussels and their broth in the middle of the table, with the lid as a bowl for the empty shells. Place the fries in a tall bowl on their own and the cold mayonnaise in a small bowl alongside. Each diner ladles mussels with broth into a deep plate, cracks the first mussel free and uses the empty shell halves as tweezers for the rest. The fries are dipped in the mayonnaise along the way, never in the mussel broth.