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Use ground espresso coffee. Regular coffee will not taste right. You can get it at the grocery next to regular coffee.

1tbsp. espresso for every 3oz. water

3c. is a lot since a single serving is usually only 1.5oz.

I know they do have the special expensive expresso coffee for those but I assume you can use any however I offer no guarentees. You would probably use two to three times the amount of coffee per cup of expresso that you would for regular coffee.