Cut the brownies into small bite-sized pieces. Set aside a few pieces for layering and topping
In a medium bowl, whisk together the sweetened condensed milk, cocoa powder, peanut butter, powdered sugar, and vanilla until smooth
Pour the cold heavy whipping cream into a large bowl. Beat with an electric mixer until firm peaks form. Do not overbeat
Gently fold about one-third of the whipped cream into the chocolate mixture to loosen it
Fold in the remaining whipped cream in two additions. Use a rubber spatula and mix gently until no large streaks remain
Fold in most of the brownie pieces and the mini chocolate chips, if using
Spread half of the mixture into a freezer-safe loaf pan or container. Drizzle with some fudge sauce and add a few brownie pieces
Add the remaining ice cream mixture and repeat with more fudge sauce and brownie pieces.
Use a butter knife to gently swirl the fudge sauce through the top. Do not overmix.
Cover tightly and freeze for at least 6 hours, preferably overnight
Let the ice cream stand at room temperature for 5 to 10 minutes before scooping. Serve with extra brownie pieces, fudge sauce, or whipped cream if desired
