Preheat the oven to 350°F (175°C). Grease a 9×13 inch baking dish with butter or non-stick spray.
In a large bowl, cream together the softened butter, granulated sugar, and light brown sugar until light and fluffy, about 3 minutes.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the semisweet chocolate chips and chopped walnuts if using.
Spread the cookie dough evenly into the prepared baking dish, smoothing the top with a spatula.
Bake in the preheated oven for 30 to 35 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with a few moist crumbs.
Remove from the oven and allow to cool for 10 minutes before serving warm.