The recipe for the chocolate cake part is here. You're best off finding your own icing, because I winged it, trying to use up cream cheese and heavy cream. I often go to Martha Stewart for things like that because her recipes usually work.
So here's your set of directions for a fast last minute Halloween cake:
1. Bake the cake. Be very careful taking it out of the pan. It sticks. Also, it will stick to whatever you place it on once you remove it, so choose well.
2. While the cake is baking, whip up your icing. You could even use canned. I won't tell. Then add your food coloring. My
3. I make my life easier by frosting only the middle and top. So basically I put the bottom of the cake on a plate, then slather on half the frosting, then press the next layer gently on top and slather on the other half of the frosting. It's cool with this cake, because then you can see the layer of orange in between the dark brown cake layers and it looks more Halloween-y (shut up, it's a word) than just frosting the whole thing in orange.
4. Grab a few squares of chocolate. I used 3 squares of Ghiradelli 60% cacao because that's all I had. Use whatever you like. Microwave it for 30 seconds, stir, check for melting. Repeat until your chocolate is melted.
5. With a steady hand and a spoon, carefully draw a jack o' lantern on the orange surface. Pumpkin lines are optional.
6. EAT. Because of course, it's not like you'll have a slew of candy to contend with in the next few days or anything.