Get out and measure your ingredients.
Place the brown sugar, heavy cream, and butter into a medium-sized saucepot.
Place the pot over medium-low heat, start whisking immediately so the sugar doesn’t burn. Once the butter melts it will become smooth, stirring occasionally, bring it to a boil, reduce to a simmer, add cinnamon and simmer for 2 minutes until slightly thickened. Take off the heat.
Reserve 2 tablespoons of the milk. Whisk the remaining milk into the pot, set aside.
Place a fine-mesh strainer over a large bowl, set aside.
In a bowl, add cornstarch, egg yolks, and salt.
Whisk until smooth.
Stream the egg mixture into the pot while whisking. Place the pot back on the stove over medium-low heat, whisking constantly so it doesn’t scorch on the bottom. The mixture will thicken to a thick pudding-like consistency.
Immediately pour the custard over the strainer and bowl, you will need to do this a little at a time, you will need to use a spatula to press the custard through the strainer.
The step with the strainer is to make sure the custard is completely smooth. There is a chance the egg may cook slightly and leave a few small chunks, this is why we strain. If you don’t mind that you can skip this step entirely.
Don’t forget to scrape the custard off the bottom of the strainer when you are done.
Stir custard until blended. Whisk the vanilla into the custard.
Pour this mixture into the baked pie crust and smooth out the top. Allow to cool to room temperature. Cover with plastic wrap and place inside your fridge for at least 6 hours, if not overnight, and set.
Serve with whipped cream, butterscotch chips, and butterscotch sauce.