Preheat the oven to 350°F. Spray a 9x13 baking dish with cooking spray, set aside.
In a large bowl add the blueberries, raspberries, blackberries, sliced strawberries, sugar, cornstarch, lemon zest, lemon juice, and vanilla extract.
Gently stir to combine so all the berries are coated in the mixture. Try not to damage the berries too much.
Spread the berry mixture into the prepared baking dish.
In a large bowl stir together the flour, sugar, brown sugar, lemon zest, baking powder, baking soda, and salt. Make sure to break up any clumps from the brown sugar if there are any, I like to use a fork to smash them.
Add the cold butter, you can either dice this into small pieces, or I like to grate it which I think is easier. Toss the butter with the flour mixture.
Using a pastry cutter or you can also use a fork, cut the butter into the mixture until the butter is cut into small pieces no bigger than a pea.
Add ⅓ cup of the buttermilk and stir it together until combined, this will be a slightly sticky wet dough.
Take a few tablespoons of the dough and flatten it out to about 1/4th inch thick. Lay the pieces of dough on top of the berries. I like to leave some of the berries exposed for a pretty presentation.
Brush the dough topping with the remaining buttermilk using a pastry brush.
Sprinkle the decorators sugar on top of the dough, if some gets on top of the berries that’s okay.
Bake for 45-50 minutes until the topping is golden brown and it’s bubbly along the edges.
If you are not sure if it is done, you can poke the topping with a toothpick, if it comes out clean it’s ready.
Let cool for at least 10 minutes before serving.
Notes
You can use various toppings on this cobbler, some of my favorites include ice cream, whipped cream, caramel sauce, creme anglaise, or even vanilla yogurt.
Add ½ teaspoon of almond extract, strawberry extract, orange extract, or lemon extract to the filling for more depth of flavor. It is always fun to mix it up!
Some people are not a fan of blackberries since they tend to have larger seeds which are hard to eat. If you are serving this at a party or get together where you are not sure of individual tastes, I would leave the blackberries out and add more of another berry.
The filling will thicken as it cools.
This can be frozen, see how to do that above.
You can use frozen berries, see how we do that above.