Sometimes when you are cooking you simply want to thicken a liquid. Traditionally, you would use flour or corn starch, or reduce the liquid over heat. Using modernist ingredients you can accomplish this same thing without diluting the flavor or changing the composition by adding heat. One of the easiest to use is xanthan gum.
In this recipe I use xanthan gum to thicken milk to emulate a banana milk shake. There are several advantages to this method over using ice cream to create a milk shake. You can use skim milk in this recipe and the taste does not change much, so you can have a very low fat milk shake. The milk shake also will not "melt" like a real milk shake would.
I went with about 0.15% xanthan gum by weight, or about 1 gram for every 600 milliliters (~2.5 cups) of milkshake. I added some vanilla extract and cinnamon for extra flavor. You can make the milk shake an hour or so ahead of time and then blend in the ice cubes right before serving.
If you like this recipe you can get more than 80 other recipes from my book Modernist Cooking Made Easy: Getting Started. The book covers many of the popular modernist techniques such as gelling, spherification, and foams. It also explores modernist ingredients like agar, sodium alginate, tapioca maltodextrin, and xanthan gum. It is all presented in an easy to understand format and I think it's the best way to learn about modernist cooking.
Also, if you are just getting started experimenting with molecular gastronomy and modernist cuisine then I highly recommend one of these molecular gastronomy kits. They have everything you need to do many different dishes.
Grind together the sugar and xanthan gum, preferably using a mortar and pestle or a fork and bowl.
Add the milk to a blender and while blending sprinkle in the sugar and xanthan gum mixture.
Add the banana and blend until well combined. Add the vanilla and cinnamon to taste and blend to combine. Just before serving add the ice cubes and blender until everything is well combined.
You can either serve the milk shake in a typical milk shake glass, or as an amuse-bouche before a meal.