Line an 8-inch sqaure pan with aluminum foil (leave an overhang). Lightly grease foil.
Add all ingredients except for the cookie butter to a saucepan and bring to a boil. Reduce to a simmer and stir in the cookie butter.
Continue simmering on low heat until the fudge has thickened to the consistency of thick caramel sauce. Immediately pour into the prepared pan and allow to cool.
Cool fudge completely for several hours before slicing into small squares. Place in the refrigerator to speed up the cooling process, if you like. Keeps in the fridge for up to two weeks.
Video
Notes
Tips
If you want to slice the fudge into perfectly neat squares, I recommend lining your pan with aluminum foil, leaving an overhang. Lift out the entire piece of fudge onto a chopping board to slice into neat pieces.
Either crunchy or creamy cookie butter is fine in this recipe. It comes down to pure preference for either very soft and creamy fudge or one with a little bit of crunch.
I use evaporated (unsweetened) milk in this recipe, because there's already a lot of sugar going into the fudge. Do not use sweetened condensed milk.
Storage
Store in an airtight container in the fridge for up to 2 weeks, or in the freezer for up to 3 months.