How to Make It
To prepare ice-cream base, combine 1/4 cup milk and cornstarch in a small bowl, stirring with a whisk. Combine remaining 1 3/4 cups milk, half-and-half, 1/4 cup sugar, and salt in a small saucepan. Bring to a simmer over medium heat. Cook 4 minutes, stirring frequently (do not boil). Add cornstarch mixture to milk mixture; simmer 2 minutes or until thickened, stirring frequently. Pour milk mixture into a medium bowl; set aside.
Combine coffee, cocoa, and remaining 1/4 cup sugar in pan over medium heat; bring to a simmer, stirring to dissolve sugar. Remove from heat; add chocolate, stirring until chocolate melts. Add cocoa mixture to milk mixture, stirring to combine. Place bowl in an ice water-filled bowl. Stir occasionally for 50 minutes or until completely cooled.
To prepare brittle, line a baking sheet with parchment paper.
Combine corn syrup, 1/3 cup sugar, and 4 teaspoons water in a small heavy saucepan over medium heat, stirring just until combined. Bring to a boil. Add chopped peanuts, peppercorns, and red pepper, if desired. Cook over medium heat, without stirring, until a candy thermometer registers 305°. Remove from heat, and stir in baking soda (mixture will bubble). Quickly pour mixture onto prepared pan; spread to a thin layer. Cool completely. Break brittle into bite-sized pieces. Set aside 1/4 cup brittle.
Pour ice-cream base into the freezer can of an ice-cream freezer; freeze according to manufacturer's instructions. Add brittle, stirring until combined. Spoon ice cream into a freezer-safe container; cover and freeze 1 hour or until firm. Sprinkle with reserved 1/4 cup brittle.