Finally got some good agave nectar and followed the recipe exactly—much better! The agave is critical to balance the acidity of the espresso and sharpness of the tequila!

I didn't have agave syrup or simple, so I substituted Licor 43, but it was too acidic and sharp (might have been the light-roast African beans I had on espresso).

Adding a splash of white creme de cacao improved the texture and the flavor! Still not perfect, though. I'll have to get some agave nectar.