You can make the pate brisee two ways: in a food processor, or by hand, as I did. I will give you both ways here. To make the pate brisee in a food processor, add the flour, cornmeal, salt, and sugar into the bowl of the processor and pulse to combine. Add the butter, and pulse until the mixture looks like coarse sand. About 10 pulses. Now put the machine to process and while running pour the ice water slowly and steadily through the liquid tube until the dough comes just comes together. This should happen very quickly, Martha says no more than 30 seconds.
If you are making the dough by hand, similarly put the flour, cornmeal, salt, and sugar into a large bowl. Cut the butter in with a pastry blender, or using your fingers as you would for a crumble, until you get the texture of coarse sand. When ready, pour 1/4 cup (or 60 ml) of the water in, give it a quick mix and assess the texture. Add more water if you need it. I used the full 1/2 cup (120ml) of water for my dough. Stir until just combined.
In either case, turn the dough out onto a floured work surface and pull it together to form a ball. Divide it in half, flatten to make a disk, and wrap in plastic. Refrigerate the dough for at least an hour, or you can leave it to chill for up to 1 day. Martha says this amount of dough will work for two 9-inch single crust pies, or one 9-inch double crust pie, or you can use it for 6 good-sized individual galettes as I did.
When the dough has had time to chill take one half out of the fridge, and divide it into 3 pieces. They should all be right around the same weight (approx 3-4oz each). On a floured surface, shape each piece into a ball, and roll out into a rough circle. I like to lay mine on a piece of plastic wrap and divide each rolled out piece with another piece of plastic wrap so that when I come to assemble the galettes they are already rolled, divided, and chilled individually. When you have rolled out all 6 pieces, make sure they are wrapped up and pop them back in the fridge while you assemble the filling.
Preheat the oven to 375f / 190c
To make the filling simply put the sliced strawberries, lemon juice, and sugar together in a bowl. With a fine mesh sifter, sift over the corn starch so it does not become lumpy and stir the strawberries gently. Give them a few minutes to hang out together while you take the dough out of the fridge and prepare the eggwash.
You will want to assemble the galettes on the baking tray you intend to bake them on, they are hard to move before they are cooked, so place the dough where you will bake it and add approximately 1/6 of the strawberry filling in the centre of the dough (this is approximately 1/2 cup of filling each). Fold the sides up over the filling, brush with the eggwash and sprinkle with demarera sugar. Repeat with the remaining galettes and bake for 30-35 minutes until golden brown. Allow to cool on the baking tray for a few minutes before transferring to a wire rack.
Makes 6 individual galettes.