Prepare a small 14 cm (5.5 inches) frame by lining its base with plastic wrap. You can also use small silicone molds.
Mix the pectin with 100 g (3.5 oz) of granulated sugar.
In a saucepan, combine the lemon juice, zest, and glucose syrup.
Heat over medium heat.
When the mixture is warm (around 40°C / 104°F if using a thermometer), gradually add the pectin-sugar mixture while whisking.
Bring to a boil (when it starts bubbling), then gradually add the remaining 200 g (7 oz) of sugar in 3 or 4 batches, stirring to maintain the boil.
Once all the sugar is incorporated, monitor the temperature with a thermometer. The mixture should reach 107°C / 224°F.
Remove the saucepan from the heat at 107°C (224°F), then add 1 tablespoon of lemon juice and mix well. From this point, work quickly to fill the molds, as the mixture sets rapidly. If you are using a frame, there is no problem since you will pour the preparation all at once. Pour into the prepared frame on a Silpat mat or into silicone molds. You may strain the mixture to remove the zest, but I usually leave it in as it adds flavor without affecting the texture of the pate de fruit.
Let set until the next day, preferably, but after 2 hours, the lemon pâte de fruit are already quite firm.
Unmold and roll them in granulated sugar. Place on a serving dish or store in an airtight container, separating each layer with parchment paper.