Start by making your pie crust.
In a large mixing bowl, combine flour and salt.
Next, add the diced butter cubes and cut into the flour using two forks (this may take 5 mins). The butter should be pea size.
Add the ice water one Tbsp at a time until your dough forms a ball.
Flatten dough into a disk and wrap in plastic wrap. Place in refrigerator for at least 2 hours or overnight.
Once the dough has chilled, use a rolling pin to roll the dough out onto a floured surface into a 1/8 inch piece and about 12 inches round. Transfer the dough onto a baking sheet lined with parchment paper.
For the filling:
Combined blackberries, corn starch, sugar, thyme leaves, lemon zest and juice into a medium size bowl and mix together.
Place the filling into the center of the rolled out pie crust leaving a 4 inch border. Fold the border of the dough over the edge of the filling. Brush the dough with an egg wash. Place in the oven and bake for about 30 minutes or until the crust is golden brown and firm. Allow to cool before serving. Serve at room temperature or slightly warm.