This ice cream is inspired by the Sichuan peanuts sold by Mama's Nuts at Logan Square Market. Find Sichuan peppercorns at spice purveyors such as penzeys.com, or substitute fresh coarsely ground black pepper for a less tongue-tingling version.
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.