Lemon Blackberry Crisp

4 cups fresh blackberries
2 Tbsp cornstarch
1/4 cup sugar
3 Tbsp fresh lemon juice
25 vanilla wafers, crushed
1/2 cup oats
1/2 cup firmly packed brown sugar
1/4 cup flour
1/2 tsp cinnamon
1/2 cup butter, melted
Ice Cream
Place Blackberries in a lightly greased 11x7 inch baking dish. Sprinkle with 1/4 cup sugar. Stir together cornstarch and lemon juice, stir into berries. Combine vanilla wafer crumbs and next 4 ingredients. Stir in butter until crumbly. Sprinkle over berries. Bake at 400 for 30 mins or until lightly browned. Serve with Ice Cream