Cream together the room-temperature unsalted butter and light brown sugar until smooth. Mix in the egg yolk and vanilla extract until fully integrated. Gradually stir in the flour, rolled oats, salt, and water until a dough forms. Press this dough into your pie dish evenly across the bottom and up the sides. Chill while you prepare the filling.
Preheat your oven to 350°F (175°C). Bake your crust for about 15 minutes until it's lightly golden but not fully cooked.
In a mixing bowl, whisk together four large eggs and one additional egg yolk until well blended. Gradually add in the heavy cream and whole milk while continuing to whisk. Stir in granulated sugar and all your spices for that signature custard flavor.
Carefully pour the custard mixture into your pre-baked crust for even distribution.
Return your pie to the oven and bake for approximately 30 minutes until set but slightly jiggly in the center. Allow it to cool completely at room temperature before chilling in the fridge for at least two hours.
For the optional praline topping, combine finely chopped pecans with light brown sugar, corn syrup, butter, sea salt, cinnamon, heavy cream, and vanilla extract. Cook on low heat until bubbly and thickened. Drizzle over each slice when serving.