Preheat the oven to 350 degrees F (175 degrees C). Grease a 9-inch round cake pan.

Heat brown sugar and ¼ cup butter in a saucepan over medium heat until butter melts and sugar dissolves, 3 to 5 minutes. Transfer to prepared cake pan and scatter cranberries over top.

Combine flour, baking powder, and salt in a bowl; set aside.

Beat white sugar and ½ cup butter together until light and fluffy. Add egg yolks one at a time, then vanilla extract. Fold in the flour mixture alternating with milk.

Beat egg whites with cream of tartar until stiff peaks form, then fold into batter. Spoon batter over cranberries, spreading evenly.

Bake in preheated oven for 55 to 60 minutes until a toothpick inserted comes out clean. Cool in the pan for 15 minutes, then invert onto a serving plate and let stand for 5 minutes.

Whip heavy cream until soft peaks form, then stir in confectioners' sugar and vanilla extract.