For the ice cream:
3 cups Coca-Cola Classic (two 12-ounce cans)
1 (0.25 ounce) envelope unflavored gelatin
2 tablespoons cold water
1 tablespoon corn starch
1 cup whole milk
1 cup heavy cream
1 cup evaporated milk
2/3 cup granulated sugar
2 tablespoons corn syrup
For the peanut brittle:
1/2 cup granulated sugar
2 tablespoons water
1 cup dry-roasted peanuts
Kosher salt, to taste
For the ice cream, pour the Coca-Cola into a large, flat-sided skillet and bring to a rolling boil over high heat. Continue boiling until the soda is reduced to approximately 1 cup, 15 to 20 minutes. Remove from heat and allow to cool.
In a small bowl, sprinkle the gelatin powder over the water and set aside. In another small bowl, combine the cornstarch with a few tablespoons of milk and whisk until smooth.
Combine remaining milk, cream, evaporated milk, and sugar in a medium saucepan and bring to a boil. Whisk in the corn starch slurry and return to a boil, stirring constantly. Allow the mixture to boil for 1 minute, then remove from the heat. Add the Coca-Cola reduction and moistened gelatin, and whisk until the gelatin is completely combined.
Transfer the ice cream base to a gallon-sized plastic zipper bag. Press out the air and place in a large bowl filled with ice water until cold, about 30 minutes. (The mixture can also be transferred to an airtight container and held in the refrigerator for up to two days.)
Pour the ice cream base into an ice cream maker and churn according to instructions. It can be served immediately or transferred to a freezer-safe container and chilled until firm.
When ready to make the peanut brittle, line a baking sheet with a silicon mat or parchment and set near the stove. Combine the sugar and water in a medium saucepan over medium-high heat, swirling the pan occasionally to help dissolve the sugar. Do not stir. Continue cooking until the sugar begins to turn a golden amber shade, about 10 minutes. Remove the pan from heat and stir in the peanuts. Pour the nuts out to the baking sheet. Let the peanuts cool completely before breaking into pieces.
To serve ice cream so that it resembles swirled soft serve, transfer it to a piping bag fitted with a large star tip. Freeze the bag in 15 to 30 minute increments until the ice cream is firm, as needed. Squeeze and pipe the ice cream in a circular motion into a bowl or cone.
Top the ice cream with a piece of peanut brittle before serving. For extra Coca-Cola flavor, pour soda over the top for a "double Coke float."