01 - Combine sugar and water in a small saucepan. Heat gently over medium heat, stirring constantly until sugar dissolves completely. Remove from heat and allow to cool to room temperature.
02 - Transfer raspberries to a blender or food processor. Blend until completely smooth.
03 - Pour raspberry puree through a fine mesh sieve into a bowl, pressing gently with the back of a spoon to remove all seeds and achieve a seedless mixture.
04 - Add cooled sugar syrup, lemon juice, and raspberry liqueur if using to the seedless puree. Stir thoroughly until well combined.
05 - Pour mixture into a shallow freezer-safe container. Freeze for 1 hour until partially frozen.
06 - Using a fork, scrape and stir the mixture thoroughly, breaking up ice crystals. Repeat this process every 30-45 minutes for 3 additional hours until sorbet reaches a smooth, scoopable consistency.
07 - Portion into chilled bowls or glasses. Garnish with fresh raspberries and mint leaves if desired.