Using a mixer (stand or hand), cream together softened butter and brown sugar. Add egg and vanilla extract and mix until combined.
In a bowl, sift together flour, baking powder and baking soda. Using a rubber spatula, fold 1/3 of dry ingredients into wet ingredients by hand. Repeat with 1/2 of remaining dry ingredients. When mixed, add the last portion of dry ingredients with 1/2 c chocolate chips. Mix until just combined. Do not over-mix.
Using a non-stick 8x8 baking pan (or a regular pan sprayed with nonstick spray), spread batter out evenly. Bake in preheated oven 30 minutes for chewy or 35 minutes for crunchy.
Sprinkle remaining 1/2 c chocolate chips over the top immediately. When chips melt, spread smooth over top. Cut into 16 squares and serve.