Ingredients

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

Instructions

1. Preheat oven to 350°F.
2. 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.
3. 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).
4. 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.
5. 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.
6. About 20 minutes before serving, put pie in refrigerator to soften.