Line an 8-inch-square baking pan with parchment paper, letting the excess paper hang over the sides.
Seal the cookies in a ziplock bag, then gently crush them into chunks with a rolling pin.
In a medium saucepan over medium-high heat, bring 1 inch of water to a simmer. Meanwhile, stir together the chocolate and condensed milk in a heat-safe bowl that will fit snugly over the saucepan without touching the water. Reduce the heat to low and place the bowl over the saucepan. Stir the ingredients until melted and smooth, about 6 minutes.
Fold 2 cups of the crushed cookies into the chocolate mixture, then pour it into the pan. Spread it evenly with a spatula. Gently press the remaining cookies into the fudge. Refrigerate until firm, about 2 hours. Use the parchment to lift the fudge out of the pan, and cut it into 36 pieces.