Combine butter and cream cheese in a small mixing bowl; beat until smooth. Add flour, mixing well. Stir in whipping cream. Shape dough into a ball; chill 1 hour.
Roll pastry to 1/8-inch thickness on a lightly floured surface. Cut pastry into 48 (2 3/4-inch) rounds. Place 1 teaspoon strawberry jam in center of 24 pastry rounds. Top jam-filled pastries with remaining rounds.
Moisten edges of pastry; fold in half, making sure edges are even. Press pastry edges firmly together using a fork dipped in flour. Prick tops with fork; brush with egg white, and sprinkle with powdered sugar.
Bake pastries on greased baking sheets at 425° for 15 minutes or until lightly browned.