1 cup unsalted butter, cut into small pieces (50 or so)
1 cup sugar
3 egg yolks
1 teaspoon vanilla
1 teaspoon baking powder
1/2 teaspoon salt
1 jar black cherry jam
In a food processor (or just use your finger tips), blend together the flour, butter, sugar, egg, 2 of the egg yolks, vanilla, baking powder and salt just until dough starts forming and pulling away from the sides of the bowl.
Dump the dough onto a well floured surface and finish blending with your finger tips.
Divide the dough into 1/3 and 2/3 parts, wrap in plastic, and place in the refrigerator to chill at least 30 minutes.
Lightly butter a 9 inch cake pan. Use your finger tips to fit the larger portion of dough evenly into the bottom and slightly up the sides of the pan. Fill with the jam. On a floured surface, roll the other part of the dough into a 9 inch or so circle. Place this on top and pinch the edges closed. If it breaks a bit with handling, don't worry, just pinch and smooth it together. Make a pattern with the tines of a fork on the top of the cake if you wish.
Mix the remaining egg yolk with 1 tablespoon of water and brush the top of the cake with this.
Bake in a 350°F oven for 1/2 hour. Remove from oven and allow to cool. Remove from the pan and allow to completely cool before wrapping in plastic wrap (be careful not to break the cake while wrapping - it is crumbly). Allow to sit at room temperature at least one day before enjoying.