Coarse-flake sea salt for sprinkling (preferably fleur de sel)
Preheat the oven to 325˚F. Line a cookie sheet with parchment paper.
In a saucepan over medium heat, melt the butter until it starts to brown. When the butter has browned and is ready, the foam will have subsided and it will have turned a nutty color. Watch closely so as not to burn the butter. Pour the browned butter into a medium bowl and stir in the brown sugar and vanilla. In a small bowl, whisk the flour and baking powder together. With a spoon, stir the flour mixture into the butter mixture until combined. Drop the dough by tablespoonfuls onto the cookie sheet. Sprinkle with sea salt and lightly press it into the top of cookies. Bake for 12 minutes.