Start by washing 8-10 fresh limes under cool running water. Zest 4 of the limes, avoiding the bitter white pith.

Slice the limes in half and extract the juice until you fill a 1-cup measuring cup. Strain the juice to remove pulp and seeds.

In a medium saucepan, combine sugar, water, lime juice, lime zest, and salt. Stir over medium heat until the sugar dissolves, about 3-5 minutes.

Bring the mixture to a gentle boil, then reduce the heat and simmer for 8-10 minutes, stirring frequently.

Remove from heat and allow to cool for about 10 minutes. Strain the mixture into a clean bottle or jar.

Seal the bottle tightly and store in the refrigerator. The flavors will deepen overnight.