Preheat to 350 degrees F. Grease a 15x10 inch pan or line with parchment. For thicker bars you can use a 9x13 inch pan.
Beat the butter and sugar together until light and creamy. Scrape sides of bowl and add the eggs one by one, followed by the vanilla.
In a separate bowl, whisk together the flour, baking powder, baking soda and salt.
Mix the dry ingredients into the egg mixture, then stir in the chocolate and nuts.
Spread the batter as evenly as possible into the prepared pan.
Bake for about 20 to 25 minutes (for 15x10 inch pan) or 25-30 minutes (for 9x13 inch pan) until they appear set and golden and cracks form on the top. Let cool in the pan, then cut into triangles or squares.
Notes
If you don't have a scale, make sure to fluff up the flour and stir it well before measuring.