Apple Crisp

1 cup all-purpose flour
3/4 cup rolled oats
1 cup packed brown sugar
1 teaspoon ground cinnamon
1/2 cup butter or margarine, softened
4 cups chopped peeled apples
1 cup sugar
2 tablespoons cornstarch
1 cup water
1 teaspoon vanilla extract
Vanilla ice cream, optional

In a mixing bowl, combine first four ingredients. 
Cut in butter until crumbly. 
Press half into a greased 2-1/2-qt. baking dish or a 9-in. square baking pan. 
Cover with apples. In a saucepan, combine sugar, cornstarch, water and vanilla; cook and stir until thick and clear. 
Pour over apples. 
Sprinkle with remaining crumb mixture. 
Bake at 350° for about 1 hour or until the apples are tender. 
Serve warm, with ice cream if desired