Cream together softened butter and brown sugar until light and fluffy. Mix in egg yolk and vanilla extract. Gradually incorporate flour, oats, and salt, forming a dough. Chill for 30 minutes.

Preheat oven to 375°F. Press chilled dough into a pie pan, poke holes with a fork, and bake for 12-15 minutes until golden brown. Let cool.

In a saucepan, combine milk and cream. Heat until bubbles form around the edges but do not boil, stirring occasionally.

Whisk together eggs and sugar in a mixing bowl until pale. Add vanilla, nutmeg, and cinnamon. Gradually temper by adding warm milk and cream, whisking continuously.

Pour custard mixture through a sieve into the prepared crust to remove lumps.

Lower oven to 325°F. Bake pie for 40-45 minutes, until edges are set but center is slightly jiggly. Toothpick should come out mostly clean.

Let pie cool at room temperature for 2 hours. Then cover with plastic wrap and refrigerate for at least 4 hours or overnight.

In a saucepan, combine chopped pecans, brown sugar, corn syrup, and butter over medium-low heat. Stir until melted. Add heavy cream and vanilla extract, mixing until smooth.

Drizzle warm praline sauce over chilled pie before serving. Garnish with fresh berries or a sprinkle of cinnamon if desired.