Preheat the oven to 350°F (175°C) and grease a 9×13 inch baking pan. Use nonstick spray or line the pan with parchment, leaving an overhang for easy removal.
In a large mixing bowl, combine melted butter and granulated sugar until smooth. Whisk for about 30 seconds so the sugar starts to dissolve and the mixture is glossy.
Add eggs one at a time, mixing well after each addition. Beat each egg in for about 20 seconds until fully incorporated and the batter looks slightly aerated.
Stir in flour, cocoa powder, and salt until just combined. Use a spatula and fold gently to avoid overmixing — a few streaks of flour are fine.
Fold in chocolate chips and chopped Snickers bars. Reserve a handful of chocolate chips or Snickers pieces to sprinkle on top if you like a more decorated finish.
Pour the batter into the prepared baking pan and spread evenly with a spatula. Press any loose Snickers pieces gently into the top so they stay visible after baking.
Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted in the center comes out with moist crumbs. Ovens vary; check at 25 minutes.
Let cool before cutting into bars and serving. Cooling for at least 30 minutes makes cleaner slices and helps the caramel settle.
Notes
These bars hold up well and can be refrigerated for firmer slices or warmed briefly before serving.