A Halloween riddle about dessert is:
 
Q: What do ghosts eat for dessert?
A: I scream (ice scream).
 
“I Scream” has been a Halloween dessert since at least 1956. “What do ghosts eat for dessert? Boo-berry pie and I-scream” was printed in many newspapers in 1973.
 
“I scream, you scream, we all scream for ice cream” is an old chant.
   
“What do ghosts eat for breakfast?”/“Dreaded wheat,” “What do ghosts eat for breakfast?”/“Ghost Toasties,” “What do ghosts eat for breakfast?”/“Scream of Wheat,” “What do ghosts eat for lunch?”/“Boo-logna sandwiches,” “What do ghosts eat for lunch?”/“Spookghetti” and “What do ghosts eat for dinner?”/“Ghoulash” are related Halloween riddles.
     
 
20 October 1956, The Courier-Journal (Louisville, KY), “Anyone For Ghoulash? Try It, Come Halloween,” pg. 10, col. 4:
WHIPPED-UP DESSERTS
Slayer Cake and I Scream
 
19 May 1973, Indiana (PA) Evening Gazette, “Mini Jokes,” The Mini Page, pg. 3, col. 1:
Q. What do ghosts eat for dessert?
A. Boo-berry pie and I-scream.
Jami Sullinger—Penn Run
 
26 January 1982, Aberdeen (SD) American News,  “Why not levity in long winter?” by Bob johnson, pg. 4, col. 5:
What do ghosts eat for dessert? I-scream and booberry pie.   
 
Google Groups: alt.humor
Halloween Humor - 25
Craig Bennett
10/15/98
(...)
What four things do monsters enjoy eating on Halloween?
Ghoulash and I Scream with booberry pie and ghoul-aid.
 
Google Books
Jokes, Riddles and Wisdom:
The Best Collection Ever
By Roger Kuder
San Jose, CA: ToExcel Press
2000
Pg. 54:
Q: What do ghosts serve for dessert?
A: Ice Scream.
 
30 October 2002, The Advocate (Stamford, CT), “Scary night,” pg. C4, col. 1:
Halloween is no time to be solemn, either, and silly food jokes abound, like “What do ghosts serve for dessert?”
 
Answer: “Ice scream.”
     
Google Groups: alt.creative.writing
What does a ghost eat?
omjaram
10/21/04
(...)
I know you won’t be able to resist goblin up this full-corpse meal. Bone appetit!:
 
Grains
Ghost Toasties      
Scream of Wheat
Pentagram Crackers with Poisonbury Jam      
Brain Muffins
                     
Entrees
Hungarian Ghoul Ash  
Frank ‘n’ Stein
Stake Sandwitch      
Halloweenie
Grave-y
Littleneck Clams      
Black Catfish
Warlocks and Bagels, with Scream Cheese      
                     
Side Dishes
Spook-ghetti          
Deviled Eggs
Artichokes            
Skullions
Scarrots                
Ghost Liver Pate
                   
Fruits
Adam’s Apples          
Nectarines
                   
Desserts    
I Scream
Boobury Pie              
Boo Meringue          
Ghoul Whip
Terrormisu            
Ladyfingers
Ghoulda Cheese        
Monster Cheese
                     
Beverages
Ghoul Ade
Coffin with Scream
Zombie
Apple Spider
 
26 October 2004, The Clarion-Ledger (Jackson, MS), “Getting into the spirit of Halloween,” pg. 1E, col. 5:
Q: What is a ghost’s favorite dessert?
A: Ice scream!
   
Google Books
Happy Halloween Jokes 6
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
What do ghosts serve for dessert?
Ice Scream.
 
Google Books
The Super, Epic, Mega Joke Book for Kids
By Whee Winn
Grand Rapids, MI: Zonderkidz
2016
Pg. ?:
What kind of dessert does a ghost like?
I scream!