In a medium saucepan, combine 1½ cups granulated sugar and 1½ cups water. Stir gently just once to help the sugar begin dissolving, then place over medium-high heat.
Once it starts to bubble, stop stirring completely. Let the mixture come to a rolling boil. This is when the bubbles are fast and vigorous, covering the entire surface.
Let it boil untouched for 20–30 minutes, watching closely. The liquid will first look clear, then slightly yellow, and then begin turning a rich amber or medium golden brown color.
Once the syrup has reached a caramel color you like, immediately remove from heat. Slowly and carefully pour in the remaining 1½ cups warm water. It will bubble and steam aggressively—this is totally normal.
As the bubbling settles, begin whisking or stirring until the mixture becomes smooth. If it clumps up at all (sometimes the cold water shocks the caramel), don’t panic—just return the pan to low heat and gently stir until it fully dissolves again.
Once your syrup is smooth and slightly thickened, stir in 1 teaspoon vanilla bean paste and 1 teaspoon fine grain salt. Mix until fully incorporated.
Let the syrup cool for 10–15 minutes, then pour into a clean glass jar or syrup bottle. You can store it in the fridge for up to 4 weeks or on the counter for up to 1 week (if your kitchen stays cool).