Place a large metal bowl into the refrigerator to chill for at least 20 minutes.
Remove the large chilled metal bowl from the refrigerator and add the heavy whipping cream into it. Beat with a hand mixer (or using the whisk attachment on your stand mixer) until stiff peaks form, about 2-4 minutes. Place the whipped cream into the refrigerator while you move on.
Place the chocolate chips in a microwave-safe bowl and heat in 30-second increments, stirring after each one, until melted and smooth.
In a separate medium bowl, add the sweetened condensed milk and melted chocolate. Whisk together until combined, then add the cocoa powder, vanilla, and salt. Whisk until combined and as smooth as possible (don't worry if there are a few small lumps). The mixture will be thick and resemble brownie batter.
Remove the whipped cream from the refrigerator and use a silicone spatula to fold about 1 cup of it into the chocolate condensed milk mixture. Then, pour the chocolate mixture into the remaining whipped cream and fold together until combined. Reserve a few brownie chunks to decorate the top of the ice cream in the next step, then fold the rest of the brownie chunks into the chocolate ice cream mixture.
Scoop a few large spoonfuls of the brownie ice cream mixture into the loaf pan along with a few smaller spoonfuls of the hot fudge sauce. Use a wooden skewer or butter knife to swirl the hot fudge and create ribbons as you go. Continue adding spoonfuls of brownie ice cream, hot fudge sauce, and swirling until all of it is in the loaf pan.
Press the reserved brownies into the top of the ice cream, then cover the top of the loaf pan with plastic wrap or aluminum foil. Freeze for 6-8 hours, after which the ice cream should be semi-firm, scoop-able, and ready to enjoy!