Prepare the Pan: Line an 8x8 inch square baking pan with parchment paper, lightly coat with cooking spray.

Cook the Fruit Base: Combine fruit purée, 2 cups sugar, lemon juice, and optional butter in a saucepan. Heat over medium-high until it boils, stirring constantly until sugar dissolves, about 5-7 minutes.

Add Pectin: Stir in liquid pectin once boiling. Bring back to a rolling boil and cook for 1 minute, stirring constantly.

Pour and Set: Transfer hot mixture into prepared pan. Allow to cool at room temperature for 4-6 hours or overnight.

Cut and Coat: Lift jelly slab, cut into 1-inch squares, and toss in remaining ½ cup sugar until coated.

Dry and Store: Let jellies dry on a wire rack for 1-2 hours. Store in a cool, dry place.