I prepared the cake mix according to the package directions, then I stirred in 1/4 c of brown sugar, a tablespoon of flour, 1/4 c chopped walnuts, and a tsp cinnamon.
I poured it into the greased crockpot and baked it on high for about 2 hours. The recipe said 1 1/2-1 3/4 hours. It also said to use a 4 1/2 quart crockpot, and I don't have one of those.
When I took it out to cool on a plate, it broke in half and some of the top came off:
I served it with powdered sugar: