In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt for 20–30 seconds until well combined and any cocoa lumps are broken up.

In a large mixing bowl, add the granulated sugar and light brown sugar. Pour in the melted, slightly cooled butter and whisk until the mixture looks glossy and thick, about 30–45 seconds.

Whisk in the eggs one at a time, mixing well after each addition. Then whisk in the vanilla extract, white vinegar, and 2 teaspoons of red gel food coloring. If the mixture looks pale, add up to 1 teaspoon more food coloring until you have a deep red; it will darken slightly once the dry ingredients are added.

Whisk in the milk or buttermilk until the batter is smooth. The mixture will be on the thinner side at this stage.

Switch to a spatula or sturdy wooden spoon. Add the dry ingredients in 2–3 additions, gently folding after each just until no dry streaks of flour remain. The dough will be thick, soft, and slightly sticky. Avoid overmixing to keep the cookies tender and chewy.

Cover the bowl tightly and refrigerate the dough for at least 2 hours and up to 24 hours. For puffier, neater cookies, chill closer to 4 hours. Proper chilling helps the cookies bake thick with well-defined crackles.

When ready to bake, preheat the oven to 350°F (175°C). Line 2 baking sheets with parchment paper or silicone baking mats. Place the extra granulated sugar in one shallow bowl and the powdered sugar in another for rolling.

Using a 1 1/2-tablespoon cookie scoop or slightly heaped tablespoons, portion the chilled dough. Roll each portion quickly between your palms into a smooth ball. Roll each ball first in granulated sugar to coat completely, then immediately roll in powdered sugar, coating heavily until no red shows. Place on the prepared baking sheets about 2 inches apart.

Bake one sheet at a time in the preheated oven for 10–12 minutes. The cookies are done when they have puffed, developed deep crackles, the edges look set, and the centers still appear slightly soft and underbaked. Do not overbake or they will lose their chewy texture.

Let the cookies cool on the baking sheet for 5–7 minutes, then transfer to a wire rack to cool completely. The powdered sugar will turn from slightly shiny to matte as they cool. Serve slightly warm or at room temperature.