In a large mixing bowl, pour the egg whites. Whisk until foamy, then add the cream of tartar. Whisk until soft peaks form, then add the sifted powdered sugar, a few spoonfuls at a time, whisking between each addition, until all the sugar is incorporated. Whisk until stiff peaks form. Incorporate the vanilla extract, then gently fold in the sifted flour in three batches.
Transfer the batter into an ungreased angel food cake pan. Bake the cake for 25 to 30 minutes or until the cake is golden and a toothpick inserted in the cake comes out clean. Invert the pan onto a wire rack and let the cake cool completely.
For the whipped Mascarpone
Add the Mascarpone, whipping cream and vanilla extract to a medium bowl and beat until combined and smooth. Add the powdered sugar, beat on low speed to incorporate, then increase the speed and beat until fluffy, about 2 minutes. Refrigerate until ready to use.
For the raspberry coulis
Combine the raspberries and maple syrup in a medium saucepan. Bring to a simmer over medium heat. Cook, stirring from time to time, until the raspberries start to break down and the coulis has thickened, about 5 to 7 minutes. Transfer to a jar and let cool completely. If you prefer a smooth coulis, you can also blend it using a hand blender.
To serve
To unmold the cake, run a sharp knife around the inside of the pan and lift the centre part with the cake sitting on it. Run the knife around the centre part of the cake and along the bottom to loosen it and remove the pan. Slice into 10 thick pieces.
Grill the cake pieces on the barbecue or toast in a skillet, a few seconds on each side, until light golden brown. Serve with the whipped Mascarpone and raspberry coulis and fresh raspberries.
