Heat the oven to 350° F. Grease a 9-inch x 13-inch baking pan with cooking spray. Line the pan with 2 crisscrossed pieces of parchment paper, leaving an overhang on all sides; spray the parchment with cooking spray.
In a medium saucepan, melt the butter and chocolate chips, stirring often, over medium-low heat. Cook, stirring, until melted and smooth, about 5 minutes. Remove from heat; set aside and let cool slightly.
Whisk the eggs in a large bowl. Add the sugar, brown sugar, vanilla, salt, and the chocolate mixture; stir to combine. Gently fold in the flour, cranberries, and ⅓ cup cacao nibs. Do not overmix. Spread the batter into the prepared pan and scatter the top with the remaining cacao nibs. Bake until a toothpick inserted into center comes out clean, about 40 minutes. Cool completely in the pan.
Holding both sides of the parchment overhang, lift the brownies out of the pan, transfer them to a cutting board, and cut into 24 squares.
