Line a loaf pan with parchment paper, leaving enough overhang on the sides for easy removal later. Place the pan in the freezer while you prepare the ice cream base.
In a large mixing bowl, whisk together the sweetened condensed milk, melted dark chocolate, cocoa powder, vanilla bean paste, and sea salt until smooth and fully combined.
In a separate large cold bowl, use a hand mixer or stand mixer to whip the cold heavy cream until stiff peaks form. Be careful not to overwhip.
Add about one-third of the whipped cream to the chocolate mixture and gently fold to lighten it. Add the remaining whipped cream and continue folding gently until no streaks remain and the mixture is fluffy and fully combined.
Remove the loaf pan from the freezer. Spread a layer of the chocolate ice cream mixture into the pan, then sprinkle with crushed chocolate sandwich cookies and drizzle with hot fudge or chocolate ripple sauce. Repeat the layers until all of the mixture is used.
Use a butter knife or skewer to gently swirl the chocolate ripple through the top layer. Don’t overmix, you want visible ribbons throughout.
Cover tightly with plastic wrap, foil, or an airtight lid. Freeze for at least 6–8 hours, preferably overnight, until firm and scoopable.
Let the ice cream sit at room temperature for 5–10 minutes before scooping for the creamiest texture. Top with extra chocolate ripple and crushed cookies if desired.