Prepare the Sponge Cake

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and line an 8-inch (20 cm) round cake pan with parchment paper.
2. Mix the Batter: In a mixing bowl, beat the eggs and sugar until pale and fluffy. Sift the flour, cocoa powder, and salt together, then fold into the egg mixture until well combined. Stir in the vanilla extract.
3. Bake: Pour the batter into the prepared cake pan and spread evenly. Bake for 12-15 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan before transferring it to a wire rack.

Prepare the Raspberry Compote

1. Cook the Raspberries: In a saucepan, combine the raspberries, sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the raspberries break down and release their juice (about 10 minutes).
2. Thicken (Optional): If you prefer a thicker compote, mix the cornstarch with a tablespoon of cold water and stir it into the raspberry mixture. Cook for another 1-2 minutes until thickened.
3. Cool: Remove from heat and allow the raspberry compote to cool completely. Once cooled, strain the mixture through a fine sieve to remove seeds if desired.

Prepare the Chocolate Mousse

1. Melt the Chocolate: Place the chopped dark chocolate in a heatproof bowl. In a saucepan, heat the cream over medium heat until it just begins to simmer, then pour it over the chocolate. Stir until the chocolate is completely melted and smooth. Let the mixture cool to room temperature.
2. Whip the Cream: In a separate bowl, whip the remaining heavy cream with powdered sugar, vanilla extract, and a pinch of salt until soft peaks form.
3. Combine: Gently fold the whipped cream into the cooled chocolate mixture until smooth and well combined. Be careful not to deflate the mousse.

Assemble the Entremet

1. Layer the Cake: Slice the cooled sponge cake into two even layers. Place one layer in the bottom of a 9-inch (23 cm) springform pan lined with plastic wrap or parchment paper.
2. Add the Raspberry Compote: Spread a thin layer of the raspberry compote over the cake, leaving a small border around the edges.
3. Add the Mousse: Spoon the chocolate mousse over the raspberry layer, smoothing it into an even layer. Add the second layer of sponge cake on top.
4. Chill: Refrigerate the entremet for at least 3 hours or overnight, allowing the mousse to set and the flavors to meld.

Prepare the Chocolate Glaze

1. Melt the Chocolate: Place the chopped chocolate in a heatproof bowl. In a small saucepan, heat the cream and corn syrup over medium heat until it just begins to simmer. Pour the hot cream over the chocolate and stir until smooth and glossy.
2. Glaze the Entremet: Once the mousse has set, carefully pour the chocolate glaze over the top of the entremet. Use a spatula to gently spread the glaze, allowing it to drip over the edges for a dramatic effect.