Preheat the oven to 375 degrees. Blind bake your pie crust 10 to 12 minutes. To blind bake, Line the crust with a parchment round or paper coffee filter. Fill the crust with pie weights or dried rice or beans. Bake in a preheated 375°F oven for 10 to 12 minutes. Remove the pie from the oven, lift out the paper and weights, and cool.
Whisk together milk and eggs in a medium saucepan. Add the flour, salt, and 1 cup of sugar. Whisk until the mixture is smooth. Continue whisking over medium heat until the mixture thickens. This should also take around 10 minutes.
It is best to caramelize the sugar and make the custard at the same time so neither cooks for too long. Use a low heat setting and be patient.
Place 1 cup of sugar in a cast iron skillet. Cook the sugar over medium-low heat, stirring with a wooden spoon, until golden brown and caramelized. It should take around 10 minutes. Keep warm over very low heat until the custard is thick.
Add caramelized sugar to the custard, whisking continuously. If the caramel hardens, just continue whisking over medium heat until it has melted and the mixture is smooth and thick. This should take 5-8 minutes.
Pour custard into the baked pie crust and refrigerate until chilled and set. This should take 1 to 2 hours. Serve with whipped cream if desired.