Inspired by a recipe I saw in an Australian baking magazine while on vacation, this incredibly striking cake has two layers: a dense butter cake and an airy crackling meringue, which bake together in one pan. —Posie (Harwood) Brien
Preheat the oven to 350°F. Grease two 9-inch round springform pans and line with parchment.
Cream together the butter, 3/4 cup of sugar, and vanilla until light and fluffy. Beat in the eggs, one at a time.
Fold in the flour, baking powder, salt, and milk, alternating between dry and wet. Divide the batter evenly between both pans and smooth the tops.
In a stand mixer, beat the egg whites and cream of tartar until soft peaks form. Slowly add the remaining sugar in a slow stream, while beating, and continue to beat until the meringue is thick and glossy and very stiff. Spread the meringue evenly over both pans. Smooth the top of one pan, and on the other pan, use a knife to make spikes and peaks in the meringue. Sprinkle the remaining tablespoon of sugar over top.
Bake for about 30 minutes, and then remove from the oven and let cool in the pans.
To make the filling, whip the heavy cream until it has stiff peaks. In a separate bowl, whisk together the mascarpone, passionfruit pulp, and confectioners' sugar. Fold in the whipped cream.
Carefully remove the cakes from the pans. Place the cake with the smooth meringue top on a cake stand or plate, and cover with the passionfruit filling. Top with the second cake.