Preheat the oven to 350°F (175°C) and place a rack in the center of the oven.
Line the bottom of a 9-inch springform pan with parchment paper.
Melt the dark chocolate in a microwave-safe bowl in 15-second intervals, stirring between each, then let cool slightly.
In a stand mixer bowl, whisk together sugar, eggs, vanilla extract, and salt. Beat on high speed for about 3 minutes until light and fluffy.
Reduce the mixer to medium speed and slowly stream in the melted chocolate. Mix until just combined.
Add the oil and milk while mixing, then scrape down the bowl.
Sift in the flour, cocoa powder, and baking powder. Gently fold the dry ingredients into the wet mixture until combined.
Fold in 100 g of raspberries using a spatula.
Pour the batter into the prepared cake pan.
Sprinkle the top with milk chocolate and the remaining 50 g raspberries.
Bake for 30 minutes, rotate the pan, then continue baking for 20–25 minutes until a toothpick inserted in the center comes out with a few moist crumbs.
Immediately top with the remaining 25 g raspberries after baking.
Cool for 5 minutes before loosening the edges with a knife. Remove the springform ring and let cool another 10–15 minutes before serving.