Preheat the oven to 350°F. Line a 9-inch square baking pan with parchment paper.
Whisk together the flour, baking powder, and salt in a medium bowl.
In a separate bowl, beat the eggs, 1 cup brown sugar, oil, and vanilla until smooth.
Fold the dry ingredients into the wet mixture just until combined. Stir in half of the chopped pecans.
Spread the batter in the prepared pan and bake for 20 minutes.
Mix the remaining brown sugar, melted butter, milk, 2 tablespoons flour, and remaining pecans.
Spoon the pecan mixture over the partially baked cake and return it to the oven.
Bake for another 40 to 45 minutes, or until the center is set and a toothpick shows moist crumbs.
Cool for at least 20 minutes before slicing and serving.