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 50 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. Mix until well combined.
Gradually add the dry ingredients to the wet ingredients and gently fold until just combined. Do not overmix.
In a separate clean bowl, beat the egg whites with cream of tartar using an electric mixer on medium speed until foamy.
Gradually add the remaining 50 grams of granulated sugar to the egg whites while continuing to beat until stiff peaks form.
Gently fold one-third of the meringue into the chocolate batter to lighten it. Then carefully fold in the remaining meringue until fully incorporated, maintaining as much air as possible.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
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.