Hacienda La Luz, one of several local plantations making chocolate from home-grown cacao, offers informative guided tours (a basic tour is one hour, but longer and more detailed tours are available) round the gardens and cacao plantation (the house is still lived in). You will be shown the traditional methods of turning cacao beans into chocolate, and, yep, the bit you were waiting for, the tour concludes with a chocolate drink. For a tour in English, it's wise to reserve in advance.
The hacienda is just 300m from Comalcalco’s central Parque Juárez: walk 250m west along Calle Bosada to its end at Blvd Rovirosa, turn right and you’ll see the hacienda’s white gateposts across the road.