1. As the filling is baking, make the biscuit topping: In a large mixing bowl, add the flour, sugar, baking powder and salt. Cut in the margarine. Mix in the “milk” and egg and form a soft dough.
2. On a floured surface, knead the dough four or five times and then roll to a uniform half inch thickness.
3. Cut the dough with a biscuit- or cookie-cutter into two 3×13 inch strips and a large star of David (either use a Chanuka cookie cutter, or cut your own with a paring knife).
4. Remove the Pyrex of hot blueberry filling from the oven.
5. Place one strip near the top of the pan, one near the bottom, and the star in the middle.
6. Brush the top of the biscuit dough with the egg wash, and sprinkle generously with turbinado sugar.
7. Bake until the biscuits are golden, about 15 minutes, or so.
8. Cool at least 45 minutes, to allow the filling to set, before serving.