Beat room-temperature butter and both sugars on medium-high for 3 full minutes until pale and fluffy. Scrape the bowl at the 1.5-minute mark.
Add the whole egg, egg yolk, vanilla, red gel food colouring, and white wine vinegar. Beat 30 seconds until uniformly red and no white streaks remain.
Sift in flour, cocoa powder, baking powder, bicarbonate of soda, and salt. Fold with a spatula until no dry streaks remain. Fold in white chocolate chips if using.
Cover and refrigerate dough for 30 minutes minimum.
Preheat oven to 175°C (350°F). Line two trays with parchment. Scoop 2-tablespoon balls, spacing 5cm apart. Bake on middle rack 10 to 11 minutes until edges are matte and set but centres look slightly glossy.
Rest on tray 5 minutes, then transfer to wire rack to cool completely.
For frosting: beat room-temperature cream cheese until smooth, add sifted icing sugar, vanilla, and salt. Beat 2 minutes until fluffy. Pipe or spread onto fully cooled cookies.