Preheat the oven to 325 degrees F. Line a baking sheet with parchment paper and draw a 9-inch circle in the middle. Grease the circle, then dust with flour, tapping off any excess.
Using an electric mixer with the whisk attachment, beat the egg whites on medium-high speed until soft peaks form. Gradually add the granulated sugar and beat for 10 minutes, or until the sugar has dissolved. Add the cream of tartar and beat for one additional minute. Gently fold in the cocoa powder and chopped chocolate. Spoon the mixture onto the circle, using a spatula to smooth the sides and top.
Place in the oven and immediately reduce the temperature to 250 degrees F. Bake for 1 hour 15 minutes to 1 hour 30 minutes, or until dry and firm to the touch. Turn off the oven and prop the oven door open with a wooden spoon. Allow the pavolva to cool completely in the oven.
When ready to serve, beat the mascarpone, heavy cream, sugar and vanilla extract on medium-high speed until the mixture is thickened and smooth.
Transfer the pavlova to a serving plate. Top with the mascarpone and fresh raspberries. Leftovers can be stored in the refrigerator for up to 2 days.