Moules-frites

Cut and soak the potatoes. Peel the 900 g potatoes to obtain about 800 g usable potato, cut into 12 mm batons and soak them in 2,000 ml cold water. Allow 30 minutes soaking. The cut potatoes are evenly sized and the soak water has turned slightly cloudy from surface starch. Use the mandoline hand guard if one is used; keep fingers away from the blade.

Dry the potatoes. Drain the potatoes, rinse once, then dry them extremely thoroughly with clean towels. Allow about 10 minutes. The potato surfaces feel dry and no droplets remain before they approach the fryer. Dry surfaces reduce dangerous spattering. Water contacting hot oil can cause violent spattering.

First fry. Heat the oil to 150 °C and fry the potatoes in two uncrowded batches, repeating with the remaining batch. Cook for about 6 minutes per batch; 2 batches. The fries are cooked through and pale, flexible at the centre and not yet browned. The first fry cooks the potato interior before crisping. Never fill the fryer more than half with oil; lower dry potatoes carefully.

Cool between fries. Spread the first-fried potatoes on a rack and cool before the second fry. Allow 15 minutes cooling. The fries are cool enough that steam is no longer visibly rising and their surfaces feel dry. Cooling lets surface moisture escape before the crisping fry.

Second fry. Raise the oil to 185 °C and fry the potatoes again in two batches, repeating with the remaining batch. Cook for about 3 minutes per batch; 2 batches. The fries are crisp, dry-sounding and evenly golden without dark burnt tips. The hotter second fry creates the crisp exterior. Keep the pot stable, never leave hot oil unattended and let used oil cool fully before handling.

Inspect the mussels. While the first-fried potatoes cool, inspect the 2,000 g live mussels, discard cracked shells and any shell that does not close when tapped, then scrub and debeard without soaking. Allow about 15 minutes. The retained mussels are closed or close when tapped, clean and free of beards. Keep shellfish refrigerated until cooking.

Sweat the shallots. Soften the 60 g shallots in 20 g butter without colouring. Cook for about 3 minutes. The shallots are soft, glossy and pale.

Steam the mussels. Add the 150 ml wine and mussels, cover and cook over high heat until the shells open, shaking the pot once. Cook for about 8 minutes. The mussel shells are open and the meat is plump and moist. Open away from your face to avoid steam; discard every mussel that remains closed.

Plate together. Fold in the 15 g parsley, portion the mussels and their liquor, and serve immediately beside the second-fried potatoes. The mussels and fries reach the table hot at the same time, with the fries still crisp. Coordination prevents either component from being held too long. Wine alcohol may remain after cooking; keep hot oil away from serving traffic.