Preheat the oven to 350°F (175°C). Grease and line an 8-inch springform pan with parchment paper.

In a bowl, whisk together flour, cocoa powder, baking powder, baking soda, salt, and sugar.

Add the egg, vegetable oil, milk, and vanilla extract. Mix until a smooth batter forms.

Pour the batter into the prepared pan and bake for 18–22 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.

In a saucepan over medium heat, combine raspberries, sugar, and lemon juice. Cook for about 5–7 minutes until the raspberries break down. Strain through a sieve to remove seeds and allow the puree to cool slightly.

In a small bowl, sprinkle gelatin over cold water and let it sit for 5 minutes to bloom. Gently heat it for a few seconds until dissolved, then mix it into the raspberry puree.

In a separate bowl, whip the heavy cream until soft peaks form.

Gently fold the raspberry mixture into the whipped cream until smooth and airy.

Pour the raspberry mousse over the cooled chocolate cake base in the springform pan. Smooth the top and refrigerate for at least 4 hours, or until set.

Before serving, garnish with fresh raspberries, chocolate shavings, and a light dusting of powdered sugar if desired.