- 1 (15- to 16-ounce) package frozen french fries
- 1 small onion
- 2 garlic cloves, forced through a press
- 3 tablespoons unsalted butter
- 2 teaspoons dry mustard
- 2 teaspoons water
- 1/2 cup mayonnaise
- 1 cup dry white wine
- 2 pounds cultivated mussels, rinsed
- 2 tablespoons chopped flat-leaf parsley
- Equipment: an adjustable-blade slicer
- Accompaniment: crusty bread (preferably a baguette)
- Cook french fries according to package instructions and keep warm in oven if necessary.
- Meanwhile, cut onion into very thin slices with slicer, then cook with garlic and a pinch of salt in butter in a wide heavy medium pot over medium-high heat, covered, stirring occasionally, until pale golden.
- While onion cooks, whisk together mustard and water until smooth, then whisk in mayonnaise and 1/4 teaspoon pepper.
- Add wine to onion and briskly simmer, covered, stirring occasionally, until onion is almost tender, about 5 minutes. Add mussels and cook, covered, stirring occasionally, until mussels just open wide, 4 to 6 minutes, checking frequently after 4 minutes and transferring as cooked to a bowl. (Discard any mussels that remain unopened.) Stir parsley into cooking liquid and season with salt. Pour liquid over mussels, then serve with fries and mustard mayonnaise.