Preheat your oven to 350°F (175°C).
Line your 9x13 inch baking pan with parchment paper, leaving some overhang on the sides.
In a medium saucepan over low heat, melt the butter and let it cool slightly.
In a large mixing bowl, whisk together the melted butter and granulated sugar until smooth. Add the vanilla extract and eggs, one at a time, whisking well after each addition.
In a separate bowl, combine the Dutch-processed cocoa, all-purpose flour, baking powder, and salt. Stir to mix.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Gently fold in the chopped Snickers candy bars. Warm the creamy peanut butter in a microwave for 15 seconds, then drop spoonfuls over the brownie batter and swirl gently.
Pour the brownie batter into the prepared baking pan and spread evenly. Bake for 25-30 minutes.
Once baked, let the brownies cool in the pan for about 15 minutes, then use parchment paper to lift them out onto a wire rack to cool completely before cutting.
