Prep the pan. Line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides to lift the fudge out later. Lightly mist the parchment with nonstick spray if you want super clean edges.

Chop the Oreos. Roughly chop the cookies so you get a mix of chunks and smaller bits. Set aside 2–3 chopped cookies for the top if you like a pretty finish.

Melt the base. In a medium saucepan over low heat, add the chocolate chips, sweetened condensed milk, peanut butter, and butter (if using). Stir constantly until the mixture is smooth and glossy. Keep the heat low to avoid scorching.

Flavor it. Remove from heat and stir in vanilla and sea salt. Taste carefully (it’s hot) and adjust the salt if needed.

Fold in cookies. Let the mixture cool for 1–2 minutes so it’s not piping hot, then fold in most of the chopped Oreos. Don’t overmix—you want visible swirls and chunks.

Spread and top. Scrape the fudge into the prepared pan. Smooth the top with a spatula. Sprinkle the reserved Oreo pieces over the surface and gently press them in. Add a light pinch of flaky sea salt for contrast.

Set the fudge. Refrigerate for at least 2–3 hours, or until firm enough to slice. For best texture, aim for 4 hours or overnight.

Slice cleanly. Lift the fudge out using the parchment. Use a warm, sharp knife (run under hot water and wipe) to cut into small squares. This stuff is rich, so 1-inch pieces go a long way.