Place the berries in a large bowl and sprinkle over the 3/4 cup sugar, cornstarch and lemon juice. Use your fingers to toss the berries so that they are coated with the sugar mixture. Turn the berries into a deep 9-inch round baking dish (or use an oval one of similar size).
Place the flour, 1/3 cup sugar, lemon zest, baking powder, baking soda, salt, cinnamon in a food processor and pulse to combine. Add the butter and pulse until the mixture resembles coarse crumbs. Turn the mixture into a bowl, pour in the milk, and stir just until a dough forms. Lightly flour a clean surface and turn the dough onto the surface and pat it into a 6 or 7-inch round. Cut the dough into 6 wedges, like a pizza. Carefully transfer the dough to the top of the berries. Arranging the wedges so that berry filling peeks from between each of the pieces of dough (see the photos if this isn’t clear!).
Lightly brush the tops of the dough wedges with milk, and lightly sprinkle them with sugar. Bake for about 40 minutes, until the dough is golden brown and cooked through and the berry filling is bubbling.
Cool on a wire rack until just warm, and serve with whipped cream or ice cream.