In a dry skillet over medium heat, toast the sesame seeds until they are golden brown and fragrant, about 3-5 minutes. Stir constantly to avoid burning.
Remove from heat and set aside.
In a medium saucepan, combine the honey (or sugar), water, lemon juice (if using), and a pinch of salt (if using).
Cook over medium heat, stirring occasionally, until the mixture comes to a boil.
Reduce the heat to low and simmer until the mixture thickens and reaches a soft ball stage (about 235°F or 112°C on a candy thermometer), which takes about 10-15 minutes.
Once the syrup has reached the desired consistency, remove it from the heat.
Quickly stir in the toasted sesame seeds, mixing thoroughly to coat all the seeds with the syrup.
Grease a baking sheet or a large plate with vegetable oil to prevent sticking.
Pour the sesame seed mixture onto the greased surface.
Use a greased spatula or your hands (be careful, as the mixture will be hot) to spread and flatten the mixture into a thin layer, about 1/4 inch (0.6 cm) thick.
Allow the mixture to cool for a few minutes until it is firm but still pliable.
Cut the sim-sim into small squares or diamond shapes using a sharp knife or a greased cutter.
Let the pieces cool completely until they harden.
Once cooled and hardened, transfer the sim-sim pieces to an airtight container for storage.
Enjoy your meal!