Frozen Lemon Gingersnap Pie

• 1 1/2 cups finely crushed gingersnap cookies (6 ounces)
• 5 tablespoons unsalted butter, melted
• 2 tablespoons sugar

• 1 1/2 cups heavy cream
• 1 cup whole milk
• 3/4 cup plus 2 tablespoons sugar
• 4 teaspoons finely grated fresh lemon zest
• 1/8 teaspoon salt
• 6 large egg yolks
• 2/3 cup fresh lemon juice

• Special equipment: an instant-read thermometer; an ice cream maker
• Garnish: lemon slices

Make crust:
Preheat oven to 350°F.

Toss together all crust ingredients with a fork until crumbs are moistened. Press evenly onto bottom and up side of a 10-inch glass or ceramic pie plate (6-cup capacity). Bake crust in middle of oven 7 minutes, then cool on a rack.

Make ice cream:
Bring cream, milk, sugar, zest, and salt to a boil in a 2-quart heavy saucepan, stirring until sugar is dissolved. Whisk yolks in a bowl until blended, then add hot cream mixture in a slow stream, whisking. Transfer custard back to saucepan and cook over moderately low heat, stirring constantly with a wooden spoon, until thick enough to coat back of spoon and registers 175 to 180°F on thermometer, 3 to 5 minutes (do not let boil).

Immediately pour through a fine-mesh sieve into cleaned bowl, then stir in lemon juice. Cool custard to room temperature, stirring occasionally, then chill, its surface covered with a round of wax paper, until cold, about 3 hours. Freeze custard in ice cream maker.

Spread ice cream evenly in crust and wrap pie plate in wax or parchment paper, then in plastic wrap. Freeze until firm, at least 2 hours.

About 20 minutes before serving, put pie in refrigerator to soften.

Cooks' notes: ·Ice cream can be made 2 days ahead of assembling pie. Soften in refrigerator about 30 minutes before spreading in crust.
·Assembled pie can be frozen up to 3 days.