Place the sugar in the sacepan. Turn heat onto medium-low.
Allow the sugar to melt, it will start to melt around the edges. Stir gently, allowing the sugar to melt evenly.
Once the sugar is almost completely melted, it will be an amber color, add the butter.
Whisk in the milk gradually, it will bubble and boil.
Bring to a rolling boil (see note) and boil for 2 minutes.
Off heat, add baking soda and cinnamon.
Whisk to mix together, the syrup will bubble and foam vigorously.
Let rest for a few minutes to let the foam settle down.
Serve warm or cold.
Store in an airtight container (like a mason jar) in the fridge, reheating and stirring before use to melt and combine.
A 2.5 quart saucepan is the smallest size you will want to use for this recipe. It will bubble and foam up quite a bit once the baking soda is added.A rolling boil is a boil that does not break even when you stir the liquid. It will take about 5 minutes to get the mixture to a rolling boil. I set a timer for the 2 minute boil step.