Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9×13 inch baking pan or line it with parchment paper for easy removal of the cookie bars.

Mix the Wet Ingredients: In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Mix until smooth. Add the eggs and vanilla extract to the sugar mixture and beat until fully combined.

Combine the Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the Chocolate Chips: Stir in the semi-sweet chocolate chips until evenly distributed throughout the dough.

Spread the Dough: Evenly spread the cookie dough in the prepared baking pan, smoothing out the top with a spatula.

Add Toppings: Sprinkle the milk chocolate chips and optional chopped nuts over the top of the dough for a decorative touch.

Bake: Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean or with just a few crumbs.

Cool and Cut: Allow the cookie bars to cool completely in the pan on a wire rack. Once cooled, cut into bars or squares.