Preheat the oven to 170°C (340°F). Grease and line an 8-inch (20 cm) round cake pan with parchment paper.
In a medium bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Set aside.
In a large bowl, whisk the egg yolks with 75 grams of granulated sugar until the mixture becomes pale and slightly thickened.
Add the whole milk, vegetable oil, and vanilla extract to the egg yolk mixture and whisk until combined.
Gradually fold the sifted dry ingredients into the wet mixture using a spatula until just combined. Do not overmix.
In a separate clean bowl, beat the egg whites with an electric mixer until foamy. Add the cream of tartar and continue beating.
Gradually add the remaining 75 grams of granulated sugar to the egg whites while beating until stiff peaks form.
Gently fold one-third of the beaten egg whites into the chocolate batter to lighten it. Then fold in the remaining egg whites carefully until fully incorporated, maintaining as much air as possible.
Pour the batter into the prepared cake pan and smooth the top.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 10 minutes. Then transfer it to a wire rack to cool completely before serving.