I simmered 1 heaping tablespoon of marshmallow root and 1 level tablespoon of powdered slippery elm in 2.5 cups of water, covered, for about 10 minutes. I poured a cup of the strained tea into a jar, then poured the remaining tea into an ice cube tray to freeze for later.
When the tea in the jar cooled, I inserted my stick blender and turned it on low. As it mixed, I incorporated 1/2 teaspoon each of xanthan gum and guar gum. I kept blending on low until the mixture thickened to my liking (around 5 minutes). * Its better for the mix to be a little thicker than you'd like, since adding oil will thin it. If you're going to add more water, xanthan or guar gum, do it before you add the oil. The gums don't thicken as well once the oil is in the mix.
Last I added avocado oil, and blended until fully incorporated. I eyeballed the avocado oil, but I would guess I used 1/2 a cup.
The texture of the finished product is slimy, yet thick. Almost like a very soft set custard. I scooped mine out of the jar, but it would be less messy to apply if in a disc cap bottle. I try to make just before using, but you can refrigerate it. My mix held up well, didn't separate or thicken when I refrigerated it overnight.