Combine the butter, sugar, and buttermilk in a medium saucepan. (At least 2 quarts.) Bring to a boil over medium heat, stirring often. Make sure you scrape the sides of the saucepan with a heatproof spatula to make sure all the sugar dissolves.
Remove from the heat and stir in the coconut extract and baking soda. As you stir, it will bubble up a lot! (Think science fair volcano.)
Let it cool for about 15-20 minutes. As it cools, the bubbles will die down and it will thicken.
Notes
The recipe makes about 1 1/4 cups of syrup.
For a thicker syrup, you can let it simmer for 3-5 minutes over low heat before adding the extract and baking soda.
We like this homemade syrup best hot or warm, but it can be served at room temperature.
Leftover syrup can safely be stored in the refrigerator for up to two weeks. But if I use fresh buttermilk, I've stored it for up to a month in a mason jar.