Chocolate Fudge Marshmallow Cake

1 chocolate cake mix, made in 8x8 pan as directed

1 c. chocolate fudge sauce, slightly warmed

1 c. marshmallow fluff

2 c. cool whip, thawed

sprinkles, optional

Poke holes all over cake with fork. Pour fudge sauce over cake (it spreads easier if warmed). Let it soak in. Spread marshmallow fluff over top. Top with cool whip. Spread evenly. Refrigerate 2 hours. Garnish with sprinkles before serving, if desired.