CSA week nine - Black sapote chews, a second try

The failure of this recipe a few days ago because of my lack of attention rather than any intrinsic fault of the recipe has been bugging me. I've got one sapote left so I wanted to give it another try.

Into my brand new 1 quart saucier went:
1/2 cup sapote pulp
1/2 cup brown sugar
1/3 cup smashed walnuts (The bulk bags at Fresh Market are pretty sturdy so I left my leftover walnuts in their bag and whacked at them with my crab mallet. I figure the powdery, buttery mush would help thicken up the mix and infuse the flavor better than chunks would.)
1/2 Tablespoon salted butter
1 egg (whole instead of just the yolk to lighten it up)
1 squeeze lemon juice
1/8 teaspoon vanilla extract (messing about with cocoa and coffee with black sapote is certainly interesting, but the classic additions of lemon and vanilla aren't to be ignored.)

I brought it to a simmer, turn the heat way down and stirred constantly as it cooked and thickened up. Instead of timing it, I kept track of the temperature with a candy thermometer. I was hoping it would act like a proper confection, but the temperature stopped rising at 205 degrees. The mix was probably too shallow for a proper reading. I judged by texture and the immediate threat of burning instead.

When I was afraid to cook it any longer I spread it out on parchment paper on a sheet pan and let it cool for a half hour and then into the refrigerator for another hour. Still more of a paste than a chew. So, I am mixing in just 1/8 teaspoon of xantham gum. Huh, no change. That's odd. Xanthan gum is pretty powerful; 1/8 teaspoon should have thickened it right up. Does xanthan gum go stale? Ah well.

Flavor's not half bad, though--the raw black sapote mellowed and enriched with the molasses, citrus and vanilla notes --and the texture is thick and creamy. Call it black sapote butter-- very nice on a slice of toast.