Prepare pan. Line a 9×13‑inch baking pan with heavy foil, leaving overhanging edges to lift fudge later.
Cook base. In a large saucepan over medium heat, melt butter. Add granulated sugar, brown sugar, and evaporated milk. Stir constantly and bring mixture to a full rolling boil. Reduce heat to low and continue boiling/stirring 4–5 minutes.
Remove the saucepan from heat. Stir in semi‑sweet chocolate chips, marshmallow cream, and vanilla until smooth and fully combined.
Fold in ¾ cup of the chopped pecans, reserving ¼ cup for topping.
Pour half of the fudge mixture into the prepared pan, spreading evenly.
Place the 54 ROLO candies (in 9 rows of 6) on top of that layer, spacing evenly.
Carefully pour the remaining fudge over the ROLO layer, ensuring all candies are fully covered and top is smooth.
Sprinkle the reserved ¼ cup pecans over top, pressing gently so they adhere.
Refrigerate until fudge is completely set and chilled (several hours or overnight).
Once firm, use the foil overhangs to lift the fudge block out of the pan. Slice into 1‑inch squares.
Store the fudge squares in an airtight container in the fridge or at cool room temperature.