Place ingredients in a microwave-safe measuring cup. Cook on HIGH for 2-3 minutes, stirring after each minute, just until the sugar dissolves.
Stovetop
Add the brown sugar and water to a small saucepan over medium heat. Bring the mixture to a simmer, stirring occasionally, just until the sugar dissolves.
Once dissolved, remove from heat and cool completely before storing in an airtight container in the refrigerator.
Notes
Brown sugar syrup will keep 2-3 weeks, if refrigerated.1 "pump" of Starbucks syrup is approximately 1 tablespoon.For Brown Sugar Cinnamon Syrup: Add 1 cinnamon stick in with the brown sugar and water, then simmer for 10-15 minutes. Remove from heat and stir in 1 teaspoon of vanilla.