In a small/medium saucepan, combine the lemon juice, water, sugar, toasted sesame oil, honey or maple syrup and soy sauce. Add any optional flavourings here if you are using them. Taste and adjust the sauce here to account for the acidity of your lemons and your own personal preferences.
Place them over a low/medium heat and allow to cool for 5 or so minutes until they begin to bubble.
In a small bowl, combine the corn starch and water to form a slurry. This will prevent the corn starch from distributing unevenly or forming little gritty balls.
Once the sauce is bubbling, pour in the corn starch mix. It should begin to thicken almost immediately. Stir well to incorporate and allow to cook for a few minutes until it reaches your desired consistency. Note that it will thicken further as it cools.
Drizzle your desired amount of sauce over the tofu cubes. This batch makes a generous quantity of sauce β you can use it all on the tofu (even if it looks runny to begin with, it will thicken as it cools) or save some for drizzling over vegetables/rice.
I like to serve the lemon tofu with rice, spring onion greens and toasted sesame seeds, but you can serve it with whatever you like.