Preheat oven to 325 degrees and grease 9 x 14 sheetpan or line with parchment paper.
Using a stand or hand mixer, cream together butter and sugar until smooth. Add in cocoa powder, vanilla, eggs, and salt. Mix until creamy. Add in flour and continue mixing until incorporated and smooth.
Spread evenly onto sheetpan, spreading to all edges, even if that leaves a few gaps here and there.
Drizzle with melted cookie butter and sprinkle chocolate chunks.
Bake for 15-18 minutes, until a toothpick comes out clean.
Let cool for 10 minutes, then cut into squares and serve!