In a medium saucepan over medium heat, combine sugar and water and stir to combine. Without stirring, cook until the sugar turns an amber hue, approx 12 minutes.
While the sugar and water are cooking, warm cream in a small saucepan, do not boil. When the caramel is ready slowly whisk in the cream until the mixture is smooth, about 2 minutes. Remove from heat, whisk in butter and salt to taste.
For the root beer float:
Using 2 drinking glasses (or mason jars) dip rim in salted caramel and sprinkle with kosher salt so it sticks to the caramel. Turn glass over in the sink to remove any salt from the inside of the glass. Add 2 scoops of ice cream into each glass and add root beer. Drizzle additional caramel sauce over the top.
Good Thyme Tip - Caramel ice cream or traditional vanilla are also great options instead.
Recipe by Good Thyme Kitchen at https://www.goodthymekitchen.com/cinnamon-salted-caramel-root-beer-floats/