what you'll need:
1/2 pkg. white cake mix (9+ oz. dry mix)
1/2 c. water
2 egg whites
2 Tb. oil
2 Tb. sour cream

Mix well and pour into a 8 x 8 pan (or 8" round) that has been sprayed with non stick stuff.

For the crumb

1 c. flour
2 Tb. cornstarch
1/2 c. sugar
1 Tb. brown sugar

Whisk to combine and with a fork, stir in butter
~1/2 c. melted butter, cooled

it will make this crumbly cookie dough type stuff
top the batter with all the topping
bake @ 350*F for 40 mins.