In a medium saucepan over medium heat, add the granulated sugar. Stir constantly with a wooden spoon or heat-resistant spatula. As the sugar melts, it will begin to form amber-colored syrup. Continue stirring to prevent burning.
Once the sugar is fully melted and golden, carefully add the salted butter to the pan. Stir until the butter has completely melted and the mixture is smooth.
Slowly pour the warm heavy cream into the caramel mixture, stirring continuously. The mixture may bubble up, so be cautious. Stir until fully combined and smooth.
Add the cinnamon and kosher salt to the caramel sauce, stirring until evenly incorporated.
Allow the sauce to simmer for another 3-5 minutes, stirring occasionally, until it thickens to your desired consistency.
Remove from heat and let the sauce cool slightly. Drizzle over desserts, ice cream, or pancakes. Garnish with flaky salt for an extra touch of flavor and texture.