In a bowl, combine plum slices, corn starch, cane sugar, lemon juice and set aside.
Preheat oven to 400° and line a sheet pan. On a well floured surface, roll out pastry dough into 9¼" x 10½" rectangle. Mark a ¾" border with a knife (do not cut through the dough) and dock inside of rectangle with a fork.
Transfer dough to a baking sheet and layer plum slices on the pastry. Brush egg wash around the edges and bake tart for 15-17 minutes or until edges are puffed up and golden brown.
Let tart cool for 5-10 minutes. Heat jelly for 20-25 seconds in a microwave. and gently brush plums with jelly. Serve tart warm or at room temperature.