In a medium metal bowl, place chocolate, oil, instant coffee, salt, and orange zest. Pour ½ cup (120 grams) boiling water over top; press chocolate down so all pieces are submerged. Let stand for 2 minutes. Whisk until smooth. Whisk in vanilla. Let stand at room temperature until thick and pipable, 2 to 3 hours. (Alternatively, place bowl in an ice water bath, and stir until thick and pipable.)
Notes
For best accuracy, measure out already boiling water to use in this recipe.
Recipe by Bake from Scratch at https://bakefromscratch.com/coconut-mocha-sandwich-cookies/