If you only have extract, the general conversion rule is 1 part oil to 4 parts extract, which would mean for about 1/2 teaspoon of peppermint extract for this recipe. (organicallymandy.com)
I recommend staring with 1/4 teaspoon peppermint extract or 3 drops of peppermint essential oil and adding more later if needed. (theconscientiouseater.com)
Add in peppermint extract, salt and almond milk and blend again. (thebettyrocker.com)