Did you place your cornstarch, sugar and lemon juice in a small pan to thicken before adding the blackberries? I wouldn't chance adding more cornstarch but you may be able to add some tapioca - you'd have to experiement with it - but you can thicken the mixture before placing in your baking dish. If not I would chuck the recipe and move on to a different one.
or try this:
Berries - (all varieties - blueberries, raspberries, strawberries, cranberries, boysenberries, blackberries)
Sugar to taste (2/3 - 1 1/2 cups)
Juice of 1 lemon
TOPPING
(vary portions to the size of your cobbler)
1/3 C. Butter
1/3 C. Sugar
1 C. Flour
Salt (small amount)
Fill a baking dish 1/2 full with berries. Add sugar, mix lightly. Sprinkle w/lemon juice and set aside.
Cream 1/3 Cup sugar with 1/3 cup butter. Cut in flour and salt until crumbly. Sprinkle over prepared berries. Bake @ 350 for 45 minutes or until lightly brown. Push topping into fruit. Serve w/cream or whipped cream.
Serve as first course or as a dessert.
OR
Fruit:
4 Cups blackberries *
1/2 Cup seedless blackberry jam
2 Tablespoons quick-cooking tapioca
2 Tablespoons sugar
2 Tablespoons butter -- cut in pcs
Topping:
1 Cup all-purpose flour
2 Tablespoons sugar
2 Teaspoons baking powder
1/4 Teaspoon salt
1/4 Cup butter
2 Tablespoons milk -- (2 to 4)
1 egg
2 Teaspoons sugar
* (fresh or frozen, if frozen do not thaw)
Preheat oven to 425 degrees.
Grease a 1 1/2 quart casserole dish.
In mixing bowl, combine blackberries, jam, tapioca and sugar.
Mix well.
Scrape mixture into casserole dish and dot with butter.
Bake 15 minutes or until mixture is bubbly. Stir well.
For topping: In a large bowl, mix together flour, sugar, baking powder and salt.
Stir well. Cut in butter until mixture is crumbly.
Stir in 2 tablespoons milk and egg until blended.
Stir milk mixture into crumbs to form a stiff dough.
On lightly floured board, roll out dough to 1/2 inch thickness.
Cut out dough with cookie cutters(hearts, diamonds, circles, whatever you like).
Place cut out shapes on top of hot fruit mixture.
Sprinkle with sugar. Bake for 15-20 minutes or until fruit is hot and bubbly.
Biscuit shapes on top should be golden brown.