Preheat oven to 325°F (170°C). Line a 13×9-inch baking pan with parchment paper, letting excess extend over sides of pan; spray with baking spray with flour.

In the top of a double boiler, combine chocolate and butter. Cook over simmering water, stirring occasionally, until melted and smooth. Turn off heat, and whisk in sugars until well combined. (Mixture will not be completely smooth.) Remove from heat, and let cool slightly, 3 to 5 minutes.

In a medium bowl, whisk together flour, cocoa, and salt.

Slowly add eggs to chocolate mixture, whisking until combined. Whisk in vanilla and food coloring. Fold in flour mixture just until combined. Reserve 1 cup (about 276 grams) batter in a small bowl. Spread remaining batter in prepared pan. Spoon Cheesecake Swirl on top of batter in pan, smoothing flat with an offset spatula. Dollop reserved batter by tablespoonfuls (about 35 grams) on top of Cheesecake Swirl. Using a wooden skewer, swirl layers.

Bake until top is shiny, edges are set, center jiggles slightly, and an instant-read thermometer inserted in center registers 165°F (74°C), 40 to 45 minutes. Let cool completely in pan. Refrigerate for at least 1 hour. Using excess parchment as handles, remove from pan, and cut into bars. Refrigerate in an airtight container for up to 6 days. Let come to room temperature before serving.