Add the blueberry filling ingredients (blueberries, sugar, cornflour, thyme, lemon zest, cinnamon and salt) to a large bowl and stir to combine.
750 g fresh blueberries, 125 g soft light brown sugar, 25 g cornflour, 2 tsp fresh thyme leaves, 2 tsp lemon zest, 1/4 tsp ground cinnamon, a pinch of salt