Prepare all your equipment. Place the silicone molds on a baking sheet and keep a measuring cup nearby to fill them neatly. If you’re using a frame, pour the mixture straight from the saucepan. Line the bottom with plastic wrap.
Mix 100 g (3.5 oz) of sugar with the yellow pectin and set aside.
In a large, high-sided saucepan, combine the passion fruit coulis and mango coulis with the 400 g (14 oz) of sugar and bring to the heat.
As soon as it begins to simmer, around 50°C (122°F), sprinkle in the sugar-pectin mixture while whisking to prevent lumps.
Bring everything to a boil over high heat. Insert the thermometer probe and continue cooking until the mixture reaches 107°C to 108°C (224°F to 226°F) for a firmer pâte de fruits. Stir constantly to prevent it from sticking to the bottom of the pan.
Once it reaches 107°C (224°F), remove the saucepan from the heat and immediately add the lemon juice. Mix well.
Pour the mixture right away into the frame, or into a measuring cup with a spout to fill the silicone molds.
Let them set at room temperature for 12 hours. Unmold, then cut into squares or any shape you like if you used a frame.
Place the pieces on a baking sheet and let them dry for another 12 hours, turning them occasionally so they dry evenly.
After drying, coat them in sugar and store them in an airtight container.