Place sweetened condensed milk in the fridge to keep cold.
Beat cold heavy cream on medium in a stand mixer fitted with the whisk attachment (or using a hand mixer) until stiff peaks form.
Turn down the speed a little and pour the condensed milkinto the whipped cream. (Stir in vanilla extract now if desired).
Then, turn up the machine speed again and whip until your mixture is thick and to stiff peaks.
Now you have your ice cream base add in your mashed banana and digestive cookies. Then drizzle over thetoffee sauce and fold just a few times to create lovely streaks of toffee throughout.
Transfer your ice cream to a large resealable container and freeze at least 6 hours or overnight before scooping and serving.