Start by tossing the flour, salt, and cubed butter into a bowl (or food processor) and mix until it looks like coarse crumbs. Slowly drizzle in the cold water, just enough for the dough to come together. Secure it in a sheet of plastic wrap and let it rest in the fridge for an hour or longer.

Once chilled, lightly flour your work surface and roll the dough into a circle slightly larger than your pie dish. Carefully transfer it to a 9-inch pie plate, pressing it gently into the bottom and sides. Trim any extra dough and shape the edges however you like. Prick the bottom with a fork to prevent puffing while baking. If the dough sticks, lightly flour the rolling pin instead of the dough to keep it tender.

Protect the crust with a parchment lining, then pack it with beans or baking weights. Bake in a preheated 400ºF oven for 15 minutes, then remove the weights and bake an extra 5 minutes to set the crust. Allow it to cool completely before adding the filling.

For the filling, whisk together the cornstarch and water until smooth. Mix in the cream, egg yolks, whole egg, vanilla, cinnamon, and nutmeg, and set aside while preparing the butter-sugar mixture.

In a saucepan over medium heat, melt the butter with light brown sugar and salt, stirring constantly for a few minutes until it bubbles gently. Slowly add the warm milk, stirring continuously to keep the mixture smooth and prevent it from spilling over.

Gradually stir the cream-and-egg mixture into the butter-sugar mixture and cook over medium-low heat, stirring constantly, until it thickens into a silky, luscious custard. A silicone spatula works best here to scrape the bottom and prevent curdling.

Take the pan off the heat and stir in the butterscotch chips until completely melted and smooth. Take a deep breath, the rich caramel aroma is irresistible.

Pour the filling into the cooled crust and let it sit on the counter for a few minutes. Then transfer the pie to the fridge and chill until firm, about 8 hours or overnight, so it slices perfectly every time.