Mussels and Fries with Mustard Mayonnaise

Ingredients

• 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)

Instructions

1. 1

   Cook french fries according to package instructions and keep warm in oven if necessary.

2. 2

   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.

3. 3

   While onion cooks, whisk together mustard and water until smooth, then whisk in mayonnaise and 1/4 teaspoon pepper.

4. 4

   Add wine to onion and briskly simmer, covered, stirring occasionally, until onion is almost tender, about 5 minutes.

5. 5

   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.

6. 6

   Pour liquid over mussels, then serve with fries and mustard mayonnaise.