Directions

1. Preheat oven to 350 degrees. Brush an 8-inch square baking pan with butter; line pan with parchment paper, leaving a 2-inch overhang on two sides. Butter paper.
2. In a large bowl, whisk together butter and sugars until smooth. Whisk in eggs and vanilla. Add flour and salt; stir just until moistened. Transfer batter to prepared pan and smooth top. Arrange candies in 12 rows (2 rows per color, repeating once) on top of dough.
3. Bake until top of cake is golden brown and a toothpick inserted in center comes out clean, 45 to 50 minutes. Set pan on a wire rack and let cool completely. Using parchment overhang, lift cake from pan and transfer to a cutting board; cut into 16 squares. (To store, keep in an airtight container at room temperature, up to 2 days.)