Coarsely chop 2 of the white chocolate baking bars. Set aside; reserve for folding into cookie dough batter. Coarsely chop remaining white chocolate baking bar. Set aside; reserve for pressing into cookie dough balls. Beat sugar and butter with a stand mixer fitted with a paddle attachment on medium speed until light and fluffy, about 2 minutes. Add eggs and vanilla; beat just until combined, about 20 seconds, stopping to scrape down sides of bowl as needed.

Whisk together flour, cocoa, baking powder, baking soda, and salt in a medium bowl; add to butter mixture. Beat on low speed until smooth and combined, about 2 minutes. Add red food coloring gel; beat on medium speed until just incorporated, about 30 seconds. Fold 2 reserved chopped baking bars into batter. Cover bowl, and chill at least 2 hours or up to overnight (8 hours). 

Preheat oven to 350°F. Line 3 baking sheets with parchment paper. Remove dough from refrigerator, and unwrap. Scoop 15 dough balls by heaping tablespoonfuls; shape into 1 ½-inch balls. Arrange 2 inches apart on 1 prepared baking sheet. (Return remaining dough in bowl to refrigerator until ready to bake.) Press about one-third of the reserved chopped baking bar into tops of dough balls. Bake until tops are crackled and edges are set, about 9 to 10 minutes. Remove from oven; cool on baking sheet 15 minutes. Transfer cookies to a wire rack, and cool completely, about 30 minutes. Repeat procedure twice with remaining dough and chopped baking bar.