Place raspberries in saucepan.
Add sugar, water, and lemon juice.
Cook on medium heat until berries soften.
Mash raspberries with spoon while cooking.
Simmer for 10 minutes until mixture thickens.
Strain through fine mesh strainer.
Discard seeds, keep smooth sauce.
Return sauce to saucepan.
Add cornstarch slurry if thicker texture needed.
Cook for 2 more minutes.
Stir until sauce becomes glossy.
Remove from heat and cool.
Add peach puree for variation.
Transfer to clean jar.
Store in refrigerator up to one week.