Line a 9x5 inch loaf pan with parchment paper. Set aside.

Make the chocolate fudge. In a small bowl, combine the chocolate chips and corn syrup. Heat the heavy whipping cream in a small saucepan just until it begins to boil. Pour the hot cream over the chocolate chips and corn syrup. Let it sit for 2-3 minutes, then whisk until smooth and well combined. If needed, microwave for another 10-15 seconds, then stir until smooth. Set aside.

In a large bowl, combine the sweetened condensed milk, milk, cooled cake mix, and vanilla extract. Stir to combine.

In a separate large mixing bowl, whip the cold heavy whipping cream on high speed until stiff peaks form.

Gently fold the whipped cream into the sweetened condensed milk mixture in two additions. Be careful not to deflate the whipped cream.

Add the sprinkles and brownie pieces to the mixture and gently fold them in until evenly dispersed. Avoid over-stirring to prevent the colors from bleeding and the brownies from breaking apart too much.

Layer the ice cream mixture into the prepared loaf pan. Add about one-third of the ice cream mixture to the bottom, then drizzle about one-third of the chocolate fudge over it. Use a knife to gently swirl the fudge into the ice cream. Repeat this layering process two more times, for a total of three layers of ice cream and fudge. Sprinkle a few extra sprinkles on top if desired. Freeze for 4-6 hours, or preferably overnight, until firm. Scoop and serve.