I have a couple requesting a "gooey fudge brownie" cake for their wedding cake and I have no idea where to start. Any help would be great since they are coming tomorrow for their tasting.

I have used this recipe which is really good, also you can do a box mix. they usually have a cake-like adjustment i think. it's been a while with box mix,

1 c. flour
3/4 c. sugar
2 tbsp. cocoa
2 tsp. baking powder
1/2 tsp. salt
1/2 c. milk
1 tsp. vanilla
2 tbsp. oil
3/4 c. walnuts (optional)
3/4 c. brown sugar
1/4 c. cocoa
1 3/4 c. hot water

Mix flour, sugar, 2 tablespoons cocoa, baking powder, salt, milk, vanilla and oil in bowl. Pour into greased 8 x 8 inch pan. Combine walnuts, brown sugar and 1/4 cup cocoa in bowl. Add boiling water and mix well. Pour over batter in pan; DO NOT MIX. Bake at 350 degrees for 45 minutes. Pudding type sauce will form under brownies.

you could always do a devils food mix with chocolate pudding added to give the fudge brownie flavor and still have a real cake (also add 4 eggs, 1 c sour cream, 1 stick of softened butter, 1/2 c water and 2 c choc chips) . not sure on your style but I have a plethora of recipes I've tried esp those I got from family. HTH