Preheat the oven to 325F (160C), grease, and line one nine-inch springform pan with parchment paper.
Melt the chocolate, cocoa powder, vanilla extract, butter, and milk in the microwave using a heat-proof large bowl and 30-second increments or over a double boiler.
Use a whisk to mix the ingredients until you have a smooth mixture. If it is hot, set aside for about 5 minutes to cool slightly.
Mix in 1/2 of the sugar amount (75g).
Mix in the egg yolks until smooth.
In a separate bowl or a bowl of a standing mixer, whip the egg whites until frothy, about 30 seconds.
Gradually add the rest of the sugar (75g) and whip on high speed until you have a medium-stiff meringue. This should take about 90 seconds to 2 minutes.
Fold the meringue into the chocolate mixture.
Pour the cake batter into the prepared cake and bake on the medium oven shelf for 22-24 minutes. The cake is ready when a toothpick comes out from the edges with a few moist crumbs, and the center appears wet. Remove from the oven and allow the cake to set and cool completely.