Melt the butter in a large, heavy-bottomed pot over medium-low heat. A stainless steel 2-quart saucepan works best for even cooking and easy cleanup.

Add the brown sugar as soon as the butter is fully melted. Use a wooden spoon to stir just until the sugar is fully incorporated with the butter—no need to overmix.

Let it cook undisturbed for 3 to 5 minutes. The mixture should begin to bubble and take on a smooth, caramel-like texture. Avoid stirring during this step to help the sugar dissolve evenly.

Slowly whisk in the cream once the sugar mixture is smooth and bubbly. The mixture may bubble up—this is normal! Reduce the heat to low immediately after adding the cream.

Continue cooking on low until the syrup reaches 225°F on a candy thermometer. This ensures the perfect thickness and texture.

Remove from heat and stir in the vanilla extract and salt until fully combined.

Cool the syrup completely before transferring to a glass jar. Store it in the refrigerator and use within two weeks for best flavor and texture.