Fresh Blue Raspberry Croustade

1. Preheat oven to 425 F. Line a sheet pan with parchment paper.
2. Add the berries to a large bowl.
3. In a small bowl, mix together the granulated sugar, cornstarch, salt and lemon zest. Pour the mixture over the berries and mix gently to coat the berries.
4. Unroll the pie crust onto the prepared sheet pan. Pour the berries and sugar into a mound in the center of the pie crust, leaving about a 2 inch border around the crust. Now, pull the sides of the pie crust up slightly over the berries, crimping the dough together every couple of inches so that it will stay in place.
5. In a small bowl, whisk the egg with a bit of water. Brush the egg wash onto exposed pie crust. Sprinkle the demerara sugar over the crust that has just been egg washed.
6. Bake in the hot oven for 25 minutes; turn the pan about halfway through so that the croustade cooks evenly. When done remove pan from oven and set on a rack.
7. Allow to cool for about 15 minutes on the pan; and then pick up the parchment paper and gently lift the whole croustade to a wire rack to cool for about another 45 minutes.
8. Put the jam (or jelly) in a small microwave safe bowl and microwave it for 15 to 20 seconds, just to melt it. Use a pastry brush to gently brush the melted jam (or jelly) onto just the berries; this will give the tart an attractive sheen.

This is best enjoyed the same day, but will keep for a couple of days.