Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment paper.
In a large mixing bowl, sift together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, baking soda, and salt until well combined.
In a separate medium bowl, whisk together the eggs, whole milk, vegetable oil, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and mix with a hand mixer or whisk until just combined and smooth. Do not overmix.
Carefully add the boiling water to the batter and stir slowly until fully incorporated. The batter will be thin; this is normal.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes.
Run a knife around the edges and invert the cakes onto wire racks to cool completely before frosting or serving.