Place 400 ml buffalo milk, 400 ml fresh cream and 90 g sugar in a large saucepan over medium heat. Stir occasionally until the sugar is fully dissolved and the mixture is hot but not yet boiling.
While the milk heats, grind the 3 g mastic to a fine powder (use a mortar and pestle or crush between two spoons). In a small bowl, combine the 10 g corn flour, 50 g arrowroot and the ground mastic.
When the milk mixture is hot, remove two or three ladlesful into the bowl with the dry thickeners and whisk until you have a smooth, lump-free slurry.
Return the slurry to the saucepan and cook over medium heat, stirring constantly, until the mixture thickens and reaches a gentle boil — about 15 minutes. Continue stirring so it does not stick.
Once the mixture comes to a boil, keep it boiling for 30 seconds, then remove the pan from the heat.
Place a shallow metal baking pan directly over a medium–high burner. Ladle in about 1 cup (250 ml) of the hot pudding mixture — just enough to cover the bottom in a thin layer.
Allow that layer to cook until it browns and chars on the bottom to form a dark, deeply colored layer. Occasionally shift the pan back and forth over the burner to promote even browning. Watch closely to avoid burning beyond the desired deep brown color.
Meanwhile, if the remaining pudding in the saucepan has cooled, reheat it briefly until it is hot and pourable and comes back to a gentle boil.
Pour the reheated pudding evenly over the burned layer in the metal pan and smooth the top with a spatula or spoon.
Let the pan cool to room temperature, then cover and refrigerate for at least 6 hours (or until fully set and chilled).
To serve, cut the set kazandibi into small squares and transfer them to plates with the burned side facing up. Dust each portion evenly with the 5 g ground cinnamon.