Well this one isn't made in the crockpot, but from what you described its basically the same thing (and I bet the clean up here is easier).
Hot Fudge Sundae Cake
1 c. flour
3/4 c. sugar
2 Tbls. cocoa
2 tsp. baking powder
1/4 tsp. salt
1/2 c. milk
2 Tbls. vegetable oil
1 tsp. vanilla
1 c. chopped nuts (optional)
1 c. brown sugar
1/4 c. cocoa
1 3/4 c. hottest tap water
ice cream
Preheat oven to 350 degrees. In ungreased 9x9x2 pan, stir together
flour, sugar, 2 Tbsp cocoa, baking powder and salt. Mix in milk, oil
and vanilla with a fork until smooth. Add nuts, if desired. Spread
evenly in pan. Sprinkle with brown sugar and 1/4 c. cocoa. Pour hot
water over batter. Bake 40 minutes...let stand 15 minutes. Invert
square into dessert dish, top with ice cream and spoon sauce over each
serving. Or just eat it right out of the baking dish, hogging all of it
for yourself and share with no one!

)
It's soooo easy to make (all in one dish) and it tastes AMAZING!!! Its good for days after (just heat it the microwave). Hope this helps...