Combine sugar, honey and water in a pot and boil for 2-3 minutes. Add lemon zest.
Boil the heavy cream in a large pot. Pour in the sugar mixture and continue to cook, constantly stirring, until a brown sticky mixture is obtained. This takes about 15 minutes.
To sample, drip a few drops of the caramel onto a cool plate. If the mixture immediately becomes firm, it's done. Stir in the butter.
Line a rectangular pan (about 20x30 cm, approximately 8x12 inches) with aluminum foil, grease it, and pour in the caramel and let cool. Then turn the pan upside-down on a large board to release the caramel, and remove the foil. Cut the caramel into squares with an oiled knife. Pull the caramel squares apart from each other and let cool completely.