Preheat your oven to 275°F (135°C). Line a baking sheet with parchment paper and draw a circle about 9 inches in diameter on the paper as a guide for shaping your pavlova.
In a clean mixing bowl, add the room-temperature egg whites and a pinch of cream of tartar. Using an electric mixer, beat on medium speed until soft peaks form.
Gradually add the granulated sugar, a tablespoon at a time, while continuing to beat the egg whites. Increase the mixer speed to high and whip until the mixture is glossy and stiff peaks form, about 5-7 minutes.
Gently fold in the sifted cocoa powder and finely chopped bittersweet chocolate using a spatula. Be careful not to deflate the egg whites; the mixture should remain airy.
Spoon the chocolate meringue onto the prepared parchment paper, using the circle you drew as a guide. Create a slight well in the center to hold the mascarpone filling later.
Place the baking sheet in the preheated oven and bake for 1 hour. Once the time is up, turn off the oven and let the pavlova cool completely in the oven with the door slightly ajar. This helps prevent cracks.
In a mixing bowl, combine the mascarpone cheese, heavy cream, granulated sugar, and vanilla extract. Whip until soft peaks form and the mixture is smooth and creamy.
Once the pavlova is completely cool, gently transfer it to a serving platter. Spoon the mascarpone cream into the center of the pavlova, filling the well you created earlier.
Generously scatter fresh raspberries over the mascarpone cream. You can also add a sprinkle of cocoa powder or chocolate shavings for extra flair.
Slice into the pavlova and serve immediately. Enjoy the delightful combination of textures and flavors in every bite!