Combine 2 cups granulated sugar, 1 cup water, and 1/4 teaspoon cream of tartar in a saucepan
Stir over medium heat until the sugar dissolves
Bring the mixture to a gentle boil
Reduce the heat to low and simmer without stirring
Cook until the syrup thickens slightly, about 10 to 15 minutes
Remove from heat and let it cool
Add 1/2 teaspoon vanilla extract if desired
Store in a clean airtight container in the refrigerator