If you don't want to use guar gum, you can use whatever simple ice cream base you want, but this one works best for me. You can swap the guar gum with 1/4 teaspoon gelatin for a pretty good result.

Microwave the milk until it is very hot to the touch but be careful not to let it boil over. 3 minutes should be pretty good. In a bowl, mix the milk powder, guar gum, salt, and sugar. Whisk the powders into the hot milk to dissolve. Add the cold cream and keep whisking. You will notice it thicken slightly. Put it into the freezer until it is very cold, whisking occasionally.

Freeze in your ice cream maker to your manufacturers instructions. It will probably be pretty soft so get it into the freezer asap. Make sure your cookies are cold and break them up into chunks. Stir all your cookies into the ice cream and get it right back into the freezer.

Finally warm up your speculoos in the microwave to make it very liquid. Get your ice cream out and pour the speculoos over it. Mix it up to form the swirl. Get it back into the freezer to harden before serving!