1. Prepare Your Pan Start by lining the bottom of a glass 8×8 inch baking pan with a sheet of wax paper or parchment paper, making sure it covers the bottom evenly. Once the pan is lined, lightly coat both the pan itself and the paper with cooking spray, ensuring full coverage so the finished fudge releases cleanly later on. Set the prepared pan aside within easy reach of your stovetop.

2. Combine and Cook the Base Mixture In a medium to large saucepan, combine the butter, evaporated milk, marshmallow cream, white sugar, and salt. Place the saucepan over medium heat and bring the mixture to a full boil, stirring constantly and without pausing the entire time. Constant stirring here is essential — the mixture contains a high concentration of sugar and dairy, which can scorch on the bottom of the pan quickly if left unattended even briefly.

3. Time the Boil Precisely The moment the mixture reaches a full, steady boil, start a timer for exactly seven minutes. Continue stirring the entire time the mixture boils, without stopping, to ensure even cooking and to prevent any part of the mixture from burning against the bottom or sides of the saucepan. This seven-minute window is critical to getting the right fudge texture, so don’t be tempted to shorten it or walk away, even for a moment.

4. Split Off the Vanilla Portion As soon as the timer goes off, immediately remove the saucepan from the heat. Working as quickly as you can, since the mixture will begin to set almost right away, carefully pour exactly 1 cup of the hot mixture into a separate glass mixing bowl. Set the remaining mixture, still in the saucepan, aside to use in the next step — it will stay pourable for just a short window, so move efficiently.

5. Make the Vanilla Layer Into the glass bowl containing your reserved 1 cup of mixture, add the ½ cup of white chocolate chips along with the ¾ teaspoon of vanilla extract. Stir the mixture continuously until the white chocolate chips have fully melted and the entire mixture looks smooth, glossy, and uniform in color, with no visible streaks or unmelted chip pieces remaining.

6. Make the Butterscotch Base Layer Return your attention to the larger portion of mixture still sitting in the saucepan. Add the 1 ½ cups of butterscotch chips, 1 teaspoon of rum extract, and 1 teaspoon of butter extract directly into the saucepan. Stir everything together thoroughly until the butterscotch chips have completely melted and the mixture is smooth, glossy, and evenly combined, with a rich golden-amber color throughout.

7. Pour the Base Layer Working quickly before the butterscotch mixture begins to set, pour it from the saucepan into your prepared 8×8 pan. Use a spatula to spread it evenly across the entire pan, pushing it into all four corners so the layer is level and consistent in thickness from edge to edge.

8. Add a Wax Paper Barrier Once the butterscotch layer is spread evenly, lay a fresh piece of wax paper directly on top of it, covering the entire surface. This barrier layer is essential — without it, the softer vanilla mixture you’re about to add will sink and blend into the butterscotch layer below instead of staying distinct on top.

9. Spread the Vanilla Layer Spoon the vanilla mixture out onto the top of the wax paper you just placed over the butterscotch layer. Using a spatula, spread the vanilla mixture as evenly as possible across the wax paper, working it out toward the edges so it covers as much of the surface area as you can manage.

10. Flip the Vanilla Layer into Place Once your vanilla layer looks smooth and even across the wax paper, carefully flip the entire thing over — wax paper and all — so that the vanilla fudge ends up face-down directly on top of the butterscotch layer, with the wax paper now facing up. This motion is similar to flipping a pancake in a pan. If this step feels tricky to manage in the same pan, an easier alternative is to spread the vanilla layer onto a piece of wax paper inside a second 8×8 pan first, then lift that wax paper (with the vanilla fudge stuck to it), flip it over, and lay it directly on top of the butterscotch layer in your original pan.

11. Clean Up the Edges Once both layers are in place, use a knife or offset spatula to tidy up the edges of the fudge, smoothing out any uneven spots along the sides of the pan for a cleaner final presentation.

12. Chill Overnight Transfer the pan to the refrigerator and let the fudge chill overnight. This extended chilling time is necessary for the fudge to fully firm up and set into a sliceable texture — rushing this step will leave you with fudge that’s too soft to cut cleanly.

13. Remove and Slice When you’re ready to serve, run a straight edge, like a butter knife, around the inside edges of the pan to loosen the fudge from the sides. Carefully invert the pan over a cutting board, gently coaxing the fudge to slide out in one piece. Once it’s out of the pan, slice the fudge into small bite-sized squares, since this treat is rich and sweet enough that a small piece goes a long way.