Lobster Salad in Potato Leek Nests

Vegetable oil , for frying

2 large leek s, white parts only

2 large russet potato es, about 1 pound

2 tablespoons butter , melted

1 tablespoon all-purpose flour

Kosher salt and freshly ground black pepper Lobster Salad:

1/2 cup mayonnaise

1 tablespoon Dijon mustard

Juice and finely grated zest of 1 lemon

Pinch cayenne pepper

1/4 cup chopped chives , plus more for garnish

2 teaspoons fresh chopped tarragon leaves

3/4 pound cooked lobster meat, cut into 1-inch chunks

1 large fennel bulb, trimmed and cored, finely diced

1 rib celery, finely diced

Kosher salt and freshly ground black pepper

1 head frisee , cleaned and leaves separated

Black American caviar , for garnish, optional