In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

In another medium bowl, add the butter and melt in the microwave for 1 minute. Add the brown sugar and whisk with the melted hot butter until well combined. Stir in the mashed sweet potatoes, peanut butter, and vanilla.

Add the dry ingredients to the sweet potato mixture and mix until combined. Add chocolate chips, reserving 1-2 tablespoons to sprinkle on top, and fold in.

Scrape the batter into the prepared baking pan. Smooth the top and add a few extra chocolate chips. Bake for 20-25 minutes or until a toothpick inserted in the center comes clean.

Remove from the oven and cool completely in the pan for about 30 minutes before lifting the parchment paper and transferring it to a wire rack to cool completely, about 1 hour. Once cooled, cut into 16 squares.