To make the crust: In a large bowl or food processor, mix flour, 1/2 cup sugar and baking powder. Cut in butter as for pie dough. In a separate bowl, mix together egg yolks and sour cream and add to flour, mixing only until combined. If dough is too dry, add an extra whole egg. If dough is too soft to roll, refrigerate for 1 hour. Lightly grease a 13x9-inch pan with butter. Roll dough large enough to line the pan and come up the sides. Fit into pan, making a crimped or rolled edge. (Note: If you have leftover dough, roll it into pencil shapes to decorate the top of the filled cheesecake.)
Heat oven to 350 degrees. In a large bowl, cream 5 ounces butter with 2 cups sugar until light and fluffy. Beat in 4 egg yolks and vanilla until well incorporated. Thoroughly mix in the cheese. In a separate bowl, beat the egg whites to stiff peaks. Fold them into the cheese mixture. Pour filling into prepared pan. If you have leftover dough, roll into pencil shapes and lay them diagonally across the top of the cheesecake. Bake 50-60 minutes or until center is only slightly jiggly. Don't let the top brown. Let cool completely before serving. Refrigerate leftovers.