Hazelnut and Chocolate Pithiviers

Preheat oven to 400 °F. Cut 1 pastry sheet into 9 1/2-inch-diameter round. Transfer to heavy large cookie sheet; chill. Using electric mixer, cream butter and sugar in medium bowl until fluffy. Mix in nuts, flour and vanilla. Mix in 1 egg. Spread filling evenly over chilled pastry round, leaving 1/2-inch border at edge. Arrange chocolate pieces over filling, spacing evenly. Chill 15 minutes. Beat remaining egg to blend in small bowl. Cut second pastry sheet into 9 1/2-inch-diameter round. Brush border of filled pastry with beaten egg. Top with second pastry round, pressing edges together firmly to seal. Crimp edges decoratively. Brush pastry with beaten egg. Cut small vent hole in center. Using tip of small sharp knife, score half circles 1/2 inch apart in top of pastry, beginning at vent and ending at crimped edge. (Can be prepared 1 day ahead. Cover and refrigerate.) Bake pastry until puffed and golden brown, about 25 minutes. Cool 10 minutes on cookie sheet. Transfer pastry to platter. Serve warm or at room temperature, cutting pastry into wedges.