In a 2-quart saucepan, bring 2 cups water and sugar to a boil, stirring to dissolve. Reduce heat to low and simmer, without stirring, to make a simple syrup, for 5 minutes.
Pour the syrup into a medium bowl, stir in vanilla extract, and transfer to the freezer to let chill for 15 minutes.
Purée the raspberries with the syrup and lemon juice in a blender or food processor until smooth. Scrape the purée through a fine sieve into a bowl; discard the seeds.
Pour into a shallow non-stick cake pan or pyrex casserole dish.
Freeze until solid.
Remove from freezer and break the mixture up into pieces. In small batches, put into the blender and liquidize until smooth.
Pour into a suitable container (a loaf pan works best) and freeze again for approximately 2 hours or until solid.
Serve and enjoy!
Notes
Tip: Add rum or tequila for a fun frozen adult drink