Preheat oven to 375 degrees F. and line a baking tray with parchment paper.
Sift flour with baking powder and salt and set aside. Cream butter and sugar together until fluffy. Whisk the egg with milk and vanilla. Add flour mixture in three additions, alternating with milk mixture and blending after each addition. Wrap dough and freeze for 30 minutes.
On a lightly floured surface, roll out dough to just less than ¼-inch thick. With cookie cutter, cut out 12 circles, about 3 ½ to 4-inches in diameter, re-rolling pastry if needed. Spoon 1 tsp of mincemeat in center of each circle. Brush edges of pastry with egg wash and fold pastry over, creating a turnover-style pastry. Brush tops with egg wash. Bake for about 18 minutes, until a light golden brown.