Butter a 9x13 baking dish; fill with sliced apples and rhubarb pieces (I used frozen), about 2/3 full.
Mix:
1/2 c brown sugar
1/2 c sugar
3 Tbsp cornstarch
1 Tbsp lemon juice
1 c water
Pour over apples.
Sprinkle with topping.
Topping:
1 c flour
1 c. sugar
1 tsp baking powder
1/2 tsp salt
2 to 3 Tbsp butter or margarine
1 egg
Mix dry ingredients. Work margarine in with a fork or pastry blender. Work in egg with a fork.. Sprinkle over apples.
Bake at 350 for 45-50 minutes or until golden brown. Serve with ice cream.