Preheat oven to 350 degrees F (175 degrees C) and place rack in center of oven.  Grease and line with parchment paper an 8 inch (20 cm) square cake pan.  Set aside.

White Butter Cake: In a mixing bowl sift the flour, baking powder, and salt.  Set aside.

In bowl of your electric mixer, beat the butter until soft (about 1-2 minutes).  Gradually add the 1 cup (200 grams) sugar and beat until light and fluffy (about 2-3 minutes). Scrape down the sides of the bowl. Add the vanilla extract and beat until combined.

With the mixer on low speed, alternately add the flour mixture and milk, in three additions, beginning and ending with the flour.  

In a clean bowl of your electric mixer, with the whisk attachment, beat the egg whites until foamy.  Add the cream of tartar and continue beating until soft peaks form.  Gradually add the remaining 1 tablespoon (15 grams) of sugar and continue to beat until stiff peaks form.  With a rubber spatula gently fold a little of the whites into the batter to lighten it, and then fold in the remaining whites until combined.  Do not over mix the batter or it will deflate.

Pour the batter into the prepared pan and smooth the top with an offset spatula or the back of a spoon.  Bake in the preheated oven for approximately 30 minutes, or until a toothpick inserted in the center of the cake comes out clean.

Cool the cake on a wire rack for about 10 minutes.  Remove the cake from the pan and leave to cool completely.

Assemble:  Using a serrated knife, cut the cake horizontally into two layers.  Place one of the cake layers onto the bottom of a clean 8 inch (20 cm) square cake pan that has been lined with plastic wrap.  Lightly crush the raspberries and then spread them over the top of the cake.  Let the ice cream soften until it is spreadable and then spoon the ice cream evenly on top of the raspberries.  Cover with the remaining cake layer.  Press down to compact the cake, ice cream and berries and then cover with the plastic wrap.  Freeze the cake for at least an hour.  About 30 minutes before serving, take the cake from the freezer and remove it from the cake pan.  Place on your serving plate.  Next, whip the cream and sugar.  Either pipe or spread the cake with the whipped cream and garnish with fresh raspberries.  Dust the top of the cake with confectioners (powdered or icing) sugar. 

Note:  You need to remove the cake at least 30 minutes before serving so that the raspberries and cake have time to soften.. 

Makes one - 8 inch (20 cm) cake.

Sources:

Slater, Nigel. 'The Kitchen Diaries'. Fourth Estate. London: 2005.

Stewart, Martha. 'Martha Stewart's Baking Book'. Clarkson Potter/Publishers. New York: 2005.