Preheat oven to 350°F (175°C). Grease or line a 9x13-inch pan with parchment paper.
Brown the butter for the crust. Let cool for 5 minutes.
Mix crust ingredients: browned butter, sugar, vanilla, salt, and flour. Press into the pan and bake for 15 minutes.
Make filling: melt butter in a saucepan, add brown sugar, maple syrup, and cream. Bring to a low boil, stir constantly.
Temper the eggs: whisk the eggs in a bowl. Slowly add some of the hot filling while whisking. Return to pan and stir in pecans.
Pour topping over warm crust. Sprinkle with sea salt if using.
Bake 30–35 minutes until mostly set. Let cool fully before cutting.