Line an 8x8 inch baking pan with parchment paper, leaving overhang on two sides, and set aside.
Pour fruit juice into heavy-bottomed saucepan and warm over medium heat until it begins to simmer.
Whisk pectin and 1 cup sugar together in a bowl, then slowly stream into the simmering juice while whisking constantly to prevent lumps.
Increase heat to medium-high and bring to a rolling boil. Clip candy thermometer to side of pan and cook, stirring occasionally, until mixture reaches 223°F, about 15-20 minutes.
Remove from heat immediately when temperature is reached. Stir in lemon juice quickly, then pour into prepared pan.
Let sit uncovered at room temperature for 24-36 hours to cure and allow surface moisture to evaporate.
Spray a sharp knife with cooking spray and cut set mixture into 1.5-inch squares.
Roll each piece in remaining ½ cup sugar until completely coated on all sides.
