Whisk the flour, cocoa powder, baking soda, and salt in a medium bowl until the cocoa is evenly distributed. The mixture should look uniformly light brown with no streaks or little pockets of baking soda.

Beat the butter, brown sugar, and granulated sugar on medium speed for about 3 minutes with a hand mixer or stand mixer fitted with the paddle attachment. Stop when the mixture looks creamy and slightly fluffier, not dense or greasy.

Mix in the egg and vanilla extract on high speed for about 1 minute, scraping the bowl as needed so everything blends evenly. The mixture should look smooth and glossy with no separated butter around the edges.

Add the dry ingredients, then pour in the milk and food coloring, and mix on low just until the dough comes together. The dough will be sticky, and that is exactly what you want at this stage.

Beat in the chocolate chips on low speed only until they are distributed through the dough. The dough should stay thick and tacky, with the chips suspended throughout instead of sinking to the bottom.

Cover the bowl and chill the dough for at least 1 hour and up to 3 days. After about 1 to 2 hours, the dough will be firm and much less sticky, which makes it easy to roll and helps the cookies bake thicker and chewier.

If the dough has been chilled for longer than 2 hours, let it sit at room temperature for at least 15 minutes before shaping. This takes the hard chill off so the cookies can spread more naturally in the oven.

Preheat the oven to 350°F (177°C) and line large baking sheets with parchment paper or silicone baking mats. The lined sheets help the cookies bake evenly and keep the bottoms from sticking or overbrowning.

Scoop and roll portions of dough about 1.5 Tablespoons (30–35g) each, then place them 3 inches apart on the prepared baking sheets. Keeping the cookies evenly sized helps them finish at the same time and keeps the batch looking consistent.

Bake for 11 to 13 minutes, until the edges are set but the centers still look very soft. They may seem slightly underbaked in the middle, and that is the cue to pull them before they dry out.

If the warm cookies did not spread as much as you wanted, gently press them with the back of a spoon, then add a few extra chocolate chips on top if desired. This quick fix gives them a smoother bakery-style shape and a more generous chip topping.

Let the cookies cool on the baking sheets for 5 minutes, then transfer them to a wire rack to cool completely. They will finish setting as they cool, and that rest helps build the chewy texture.