Place flour, sugar, and salt into base of Power Chef® fitted with blade attachment. Add in half of the cut butter pieces. Cover and pull cord until butter has been cut into small pea size pieces. Repeat with remaining butter. Pour flour mixture into medium bowl and add in egg. Stir together and add cold water as necessary to make dough come together. Seal bowl and place in refrigerator until dough is thoroughly chilled, about an hour. Preheat oven to 350° F/175° C.
Bake, glaze and serve the pastry
Dust the silicone baking sheet with rim with flour and roll out dough as thin as possible on mat, between ¼–⅛″/.6–.3 cm. Straighten edges with the edge of the Silicone Spatula so the dough is a large rectangle. Cut rectangle into at least eight rectangles and use the scraps to make one more. Place about 1 tbsp. of jam onto one piece of dough and brush milk on all the edges. Place another piece of dough on top and seal with the tines of a fork. Repeat until all pastries have been made. Brush the tops of pastries with milk and pierce 2–3 times with a fork. Place onto baking sheet lined with silicone baking sheet with rim. Bake for 20–25 minutes or until golden brown. When cooled, top with glaze if desired