Pre-heat oven to 350°F. Slightly melt butter in the microwave for 30-40 seconds.

Using an electric hand mixer, beat the slightly melted butter, sugars, eggs, and vanilla extract until light and fluffy.

In a separate bowl, stir together the flour, cocoa powder, baking soda, and salt. Add into wet ingredients and stir just until combined (the batter will be thick and not overly wet). Fold in the chocolate chips and nuts until combined - reserving a few for the top if desired.

Spread batter in a 10-inch cast-iron skillet and top with any remaining chocolate chips as desired. Bake for 20-24 minutes, until edges are set. The result will be a gooey-ish center; if you want it more done in the center, add on 3-5 additional minutes, depending on your oven.

Let cool slightly; slice, and serve warm with vanilla ice cream for the yummiest result!