To brown the butter, melt over medium heat, stirring frequently. It will start to bubble. Stir constantly, and watch closely as it will begin to turn golden and then brown. Remove from heat, and allow to cool. You may want to place in fridge for 10 minutes to help it come back to a solid state. Stir it frequently. You want it to be the texture of softened butter.

Chop chocolate and nuts.

Line a heavy 13 x 9 inch baking pan with parchment, and preheat oven to 350 degrees F.

In a medium mixing bowl, whisk together flour and salt.

In another medium-size bowl cream butter with brown sugar, egg, and vanilla.

Add dry ingredients to wet, and mix just long enough to combine (you may need to use your hands).

Spread dough in prepared pan, and flatten with hands. Bake at 350 degrees for 20 minutes or until golden. Place pan on cooling rack, and immediately cover with chocolate. When the chocolate has melted, spread evenly and top with chopped pecans. Sprinkle with flaky sea salt, if desired. Allow to cool completely and chocolate to set.

Cut into squares and enjoy.