Separate the eggs. Put the egg whites in a small stainless steel or glass mixing bowl and set aside. Put the yolks in a small bowl or cup and set aside.

Preheat the oven to 350 F.

Combine the brown sugar and butter in a 9-inch round cake pan and place it in the oven. When the butter has melted, stir until smooth and cook for 3 to 5 minutes until the mixture bubbles. Remove the pan from the oven and set it on a rack.

Toss the cranberries with the orange zest and juice in a medium bowl, then sprinkle them over the brown sugar and butter mixture.

Separate the eggs. Put the egg whites in a small stainless steel or glass mixing bowl and set aside. Put the yolks in a small bowl or cup and set aside.

Mix the flour, baking powder, and salt; stir with a whisk to blend thoroughly. Set aside.

Beat the granulated sugar with 1/2 cup of butter in a mixing bowl with an electric mixer for 3 to 4 minutes until light and fluffy. Add the egg yolks, one at a time, beating well after each addition. Beat in the vanilla extract.

Add about one-third of the flour mixture to the creamed mixture and beat slowly until blended. Beat in half of the milk. Add another one-third of the flour and mix well. Beat in the remaining milk and then beat in the remaining flour mixture.

With clean beaters, beat the egg whites and cream of tartar to soft peaks.

Fold the egg whites into the cake batter.

Spread the batter evenly over the cranberry layer.

Bake the cake for 35 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Cool the cake in the pan on a rack for 15 minutes.

Invert the cranberry upside-down cake onto a cake plate.