Add the softened butter to a skillet over medium heat, and stir in the pecans. Toast the pecans for 5 minutes and set aside.
Combine the cornstarch, salt, flour, cinnamon and baking soda in a bowl.
Place the cooled brown butter into a mixing bowl with the eggs, vanilla and egg yolk. Blend until combined.
Place the dry ingredients into the egg and butter mixture, and beat until a smooth batter has formed.
Mix the toasted pecans into the dough.
Chill the dough for 4 hours in the fridge.
Heat the oven to 375 degrees, and line a baking sheet with parchment paper.
Scoop the cookie dough onto the baking sheet.
Flatten the cookies slightly, and place a pecan half in the center of each one.
Bake for 10 minutes. If not quite browned, cook a few minutes longer.
Cool before serving.
