Peach Berry Sonker

Make the dough

1. Preheat the oven to 375°F (190°C). Butter the sides of an 11-by-11-inch (27-by-27-cm) or 9-by-13-inch (23-by-33-cm) baking dish.
2. In a medium bowl, combine the flour, baking powder, salt, and pieces of cold butter. With a pastry cutter, knives, mezzaluna, or your fingers, cut and smoosh the butter into the dry ingredients until it is roughly mixed.
3. Add the milk and mix until the dough is tacky.
4. Place half the dough on a well-floured board. Pat the dough out a bit, roll it out to about 3/8 inch (1 cm) thick, and cut into long 2 1/2-inch (6 cm) wide strips.
5. Lift a strip and tuck it around the sides of the pan. Repeat with the other strips until the pan is encircled with the wide strips. It’s okay if you have to piece them together. The bottom of the pan will be doughless.

Make the filling

1. Place the flour and 1 1/4 cups granulated sugar in the baking dish and mix around a bit with your fingers or a fork to combine.☞ TESTER TIP: If your fruit is ripe and sweet, you'll probably want to reduce the amount of sugar to 3/4 cup.
2. In a medium bowl, combine the peaches, blackberries, and vanilla, and gently mix together. Turn the filling onto the flour and sugar in the baking dish.
3. Sprinkle 2 tablespoons sugar over the top of the fruit.
4. Break up the butter into small pieces and place over the top of the fruit evenly.
5. Roll out the remaining dough to 3/8 inch (1 cm) thick and cut into long 2 1/2-inch (6 cm) wide strips. Lay the strips over the top of the filling to form a rough lattice. An offset spatula is a great help in getting the rolled out strips onto the top of the filling.
6. In a small bowl, mix the egg and water together with a fork and brush some on top of the lattice strips. Sprinkle with 2 tablespoons of sparkling sugar.☞ TESTER TIP: If your baking dish seems precariously full, place it on a foil-lined baking sheet in case the filling overflows during baking.
7. Bake the sonker for 30 minutes. While the sonker is baking, make the milk dip.

Make the milk dip

1. In a medium saucepan over low heat, whisk together the cornstarch, sugar, and salt. Whisk in the milk.
2. Increase the heat to medium-high and bring to a boil while whisking constantly. Cook for 2 minutes more while whisking.
3. Remove from the heat, stir in the vanilla, and let cool.
4. After the sonker has baked for 30 minutes, carefully remove it from the oven, place it on a flat surface, and close the oven door. Pour 1/2 cup of the hot milk dip over the top.
5. Return the sonker to the oven and bake until the filling is bubbling around the edges and up through the crust, about 30 minutes more. The crust should be a beautiful golden brown when finished. If it seems to be browning too quickly, loosely place a piece of foil over the sonker and continue to bake.
6. Let cool for 20 to 30 minutes.
7. Serve the sonker warm or at room temperature, keeping in mind it’s best the day it’s made. Pass any remaining milk dip on the side (and you may even want to double the milk dip to ensure ample for drizzling). Any leftover milk dip can be refrigerated.