1½ sticks butter ¾ cup
1 cup brown sugar packed packed
½ cup milk
2 teaspoons vanilla extract
Melt butter in a medium saucepan over medium-low heat.
Add the brown sugar to the melted butter and cook, stirring constantly, for 1 minute (be sure the butter and sugar are completely combined and you can’t see any separated butter in the mixture).
Bring to a boil over medium heat. Continue cooking, stirring, for 2 minutes.
Add the milk and vanilla. Bring to a boil over medium heat. Continue cooking, stirring, for 3 minutes.
Remove from heat and set aside to cool. The longer it cools, the thicker it becomes. When it’s at your desired consistency, drizzle over the cooled cake and serve.