Preheat the oven to 350°F. Line a 9x13 baking pan with parchment paper. Lightly grease the paper. This prevents sticking and makes removing the bars easier later.

Place softened butter, brown sugar and white sugar in a mixing bowl. Beat with a mixer until light and fluffy. This step helps create soft and tender cookie bars.

Crack the eggs into the bowl one at a time. Mix well after each addition. Add vanilla extract and mix again until smooth and creamy.

In another bowl, mix flour, baking soda and salt. Stir well. Slowly add this mixture to the wet ingredients while mixing gently.

Fold chocolate chips and chopped walnuts into the dough using a spatula. Mix slowly so the chips spread evenly throughout the dough.

Place the dough into the prepared baking pan. Spread it evenly using a spatula. Make sure the dough reaches the corners of the pan.

Bake in the preheated oven for about 25 minutes. The top should look golden brown. The center should remain soft and slightly chewy.

Remove the pan from the oven. Let the bars cool completely on a rack. Once cool, cut them into squares or rectangles before serving.