Special equipment: silicone baking mat; candy thermometer
Line a half sheet pan with a silicone baking mat.
Bring the cassis puree to a boil in a pot, continuously stirring to prevent scorching. Combine 110 grams of the sugar with the pectin using a whisk, add to the fruit puree and boil for 2 to 3 minutes. Add the remaining 1000 grams sugar to the fruit puree in three or four batches, continually whisking. Then add the glucose syrup. Continue to cook, whisking, until a candy thermometer inserted in the mixture reaches 225 degrees F. Then whisk in the citric acid. Quickly pour the mixture onto the prepared sheet pan and cool the mixture completely in the refrigerator.
Cut the fruit pate into 2-by-6-inch strips and sandwich between two chocolate bars to serve.