Preheat oven to 350°F. Grease a 1+13-inch metal pan. Line the bottom with a parchment paper, Chris the paper, and flour the pan.

In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.

In a large bowl, with an electric mixer, beat the butter until creamy. Add the sugar and beat until light and fluffy, 3 to 5 minutes.

In a small bowl, whisk together the eggs and vanilla. In another small bowl, whisk together the sour cream and milk. Pour the egg mixture into the butter-sugar mixture and beat on medium speed for two minutes.

On low speed, alternate adding the flour mixture and the sour cream mixture to the butter-egg mixture, beginning and ending with the flour adding the food coloring with the addition of liquid.

Pour the batter into the prepared pan and spread evenly. Tap the pan on the worksurface to get rid of any air bubbles.

Bake till a wooden pick inserted in the center comes out clean, 25 to 28 minutes.

Cool in the pan on a wire rack for 15 minutes. If necessary, loosen