- 1 large egg white
- 1/4 cup packed light brown sugar
- 1/2 teaspoon instant coffee granules, crushed
- 1 cup walnut pieces (3 1/2 ounces), coarsely chopped if desired
- 1 cup granulated sugar
- 1/4 cup water
- 6 Tablespoons Irish whiskey
- 1/4 cup heavy cream
- 1/4 teaspoon salt
- 2 pints good-quality coffee ice cream
- Preheat oven to 325°F with rack in middle. Line a rimmed sheet pan with a nonstick baking liner, or line it with foil and lightly oil foil.
- Whisk egg white with sugar, coffee powder, and a pinch of salt in a bowl until blended. Stir in walnuts until coated. Spread mixture into a 10- by 8-inch rectangle in pan.
- Bake until crisp is dry to the touch, 20 to 25 minutes. Transfer pan to a rack to cool completely.
- Loosen crisp with a metal spatula and break into small pieces.
- Bring sugar and water to a boil in a 2-quart heavy saucepan over medium-high heat, stirring until sugar is dissolved. Boil without stirring, but washing down any sugar crystals with a brush dipped in cold water, until syrup begins to turn golden, about 5 minutes. Continue to boil, swirling pan occasionally, until syrup is a deep golden caramel.
- Remove pan from heat and carefully add whiskey, cream, and salt (mixture will bubble up and steam and caramel will harden).
- Return pan to heat and simmer, stirring, until caramel is dissolved and sauce is smooth. Cool to warm.
- Serve sauce over scoops of coffee ice cream then sprinkle with walnut crisp.