Place the empty metal bowl of a stand mixer and the whipping attachment in the freezer.
On a cutting board chop up all of the butterfinger bars. Set aside 1/4 cup of chopped butterfinger to sprinkle on top of the ice cream if desired.
In a large mixing bowl, combine together milk, condensed milk, vanilla, and salt. Set aside.
Pull the bowl out of the freezer and pour in the heavy whipping cream.
Begin whipping the cream at medium speed it should begin to thicken up around 4 minutes. Raise the speed up and continue beating the cream, after about 6-7 minutes you should get soft peaks. Which means that the cream on the whisk will stand but the tip with bend over. Continue beating the cream for only 1-2 minutes longer after you reach the soft peak stage. You want a mostly firm peak, which means it stands on its own or almost does. Stop here, if you continue on longer you will create butter.
Gently fold the whipped cream into the sweetened condensed milk mixture.
Gently fold in the cut up butterfinger bars.
Pour the mixture into a 9 x 5 x 3-inch glass or metal loaf pan.
Sprinkle on the 1/4 cup of the reserved butterfingers over the top of the ice cream. Cover really well with a tight fitting lid or plastic wrap and aluminum foil.
Freeze for 6 hours or overnight, then serve.