How to make a slice of watermelon cake topper

Watermelon Cake Finished

Here in southern Mississippi, the hot summer weather had already taken over and the watermelon patches are already producing big, bright watermelons!

Enjoying a slice of cold watermelon is one of my favorite things in the summertime, so I fell in love with this party theme. For the cake, I was asked to include the stripes of watermelon and also a bitten slice on top. Isn’t that fun?

Because of the shape of a slice of watermelon, I knew doing it from cake would be difficult, so I opted to make it with rice cereal treats. I took pics as I made it and today I want to show you how I made the slice of watermelon cake topper!

Here’s what I used:
Prepared rice cereal treats
Half ball pan (or bowl with ~6″ diameter)
Non-stick cooking spray
Large sharp knife
Small round crinkled cookie cutter (about 1.5″ or 3-4cm)
Red, white, green and black fondant
Xacto knife
Pizza wheel
Sugar glue (or water) and a small paint brush
Tiny teardrop cutter
Vegetable shortening (optional)

Step 1:
Prepare rice cereal treats. I follow the instructions on the back of the marshmallows to make these!
How to Make Watermelon Cake Topper 01

Step 2:
Spray a half ball pan with nonstick cooking spray. I use the Wilton sports ball pan set (or half of it) but you could also use a bowl of similar size.
How to Make Watermelon Cake Topper 02

Step 3:
Tightly press the rice cereal treats into the pan until it’s very firm. You’ll want to do this while the mixture is still warm so that it will be easier to press into the pan.
How to Make Watermelon Cake Topper 03

Step 4:
Once you have it packed in, flip out the half ball onto a mat and stick it in the refrigerator to chill and harden for at least 15 minutes.
How to Make Watermelon Cake Topper 04

Step 5:
After the shape has chilled, take a large, sharp knife and cut the ball in half. Then cut again to make a narrower wedge and then you’ll also have 2 very smooth sides.
How to Make Watermelon Cake Topper 05
How to Make Watermelon Cake Topper 06

Step 6:
Using a crinkle edged round cutter, you can take a “bite” out of the top of the wedge.
How to Make Watermelon Cake Topper 07

Step 7:
Get a ball of red fondant and roll it out  large enough to cover the slice. I like to roll it thick so that the bumpiness of the cereal underneath is not noticeable.
How to Make Watermelon Cake Topper 09
How to Make Watermelon Cake Topper 10

Step 8:
Lay the fondant over the wedge and smooth it down with your fingers, being careful to work it into the missing bite without tearing it.
How to Make Watermelon Cake Topper 11

Step 9:
Trim the excess fondant leaving just a very small skirt around the edges.
How to Make Watermelon Cake Topper 12

Step 10:
Tuck the edges under and smooth it down. I like to press the edges into the cereal so that it sticks and is smooth on the bottom.
How to Make Watermelon Cake Topper 13
How to Make Watermelon Cake Topper 14

Step 11:
Use a ball tool to make teeth marks in the missing bite. This step is not necessary but I love little details like this!
How to Make Watermelon Cake Topper 15
How to Make Watermelon Cake Topper 16

Step 12:
Roll out some white fondant and set the slice of watermelon on top of it. You’re going to want to trim it into the shape of a football (an American football) so that it’ll wrap up under the bottom of the watermelon slice.
How to Make Watermelon Cake Topper 17
How to Make Watermelon Cake Topper 18

Step 13:
Gently wrap the fondant underneath the slice and form it all the way to the edges. I used my Xacto knife to trim until I got it to “fit”.
*Note – I was able to gently press my fondant on to the rice cereal and it stuck with no problem. If you have trouble getting your fondant to stick, you may want to paint on a thin layer of sugar glue before attaching it to the slice.
How to Make Watermelon Cake Topper 19

Step 14:
Repeat steps 12 and 13 for the green layer of “watermelon rind”. Again, use sugar glue to attach the green to the white if it doesn’t stick on it’s own.
How to Make Watermelon Cake Topper 20
How to Make Watermelon Cake Topper 21

Step 15:
Roll out a small amount of black fondant very thin. Let it dry for 10-15 minutes so that it’s easy to cut out the small shapes.
How to Make Watermelon Cake Topper 22

Step 16:
Cut out the watermelon seeds and attach them with a tiny dot of sugar glue. Allow them to dry for a few minutes and you’re done.
How to Make Watermelon Cake Topper 24

Step 17:
I rubbed a thin layer of vegetable shortening over my entire watermelon slice after it was placed on the cake. That gave it the shiny “wet” look, but this step is not necessary if you want to skip it!
Watermelon Cake Topper

Happy Caking!



  1. there isnt the recipe or ammounts for marshmallows to prepare the rice cereal,can you please add them Rose ,thank you for your idea.Sandra

  2. Wrap the Rice Krispie shape up in the fondant and work out and seams. You can add more stripes over the green and just smooth them in. If it is getting sticky add a little powdered sugar and rub it in. If you have it outside slice it quick, the humidity make the “skin” stick together. It may not be as refreshing as a good watermelon, but you can make them year round.

  3. This was my first time with fondant, it was messy but fun! I worked the powdered sugar in but ran into trouble while rolling the fondant out. It was sticking to the counter so I sprinkled some sugar down to keep it from sticking.. It stopped the sticking but stained the dark green. I looked around and saw that a lot of people recommend either corn starch or shortening. I’ve got one to make tomorrow so I guess I need to pick one.. I went with the strawberry mallows, I was worried about seeing watermellon but tasting strawberry; however, I think the taste came out quite good. I was going to try to make it with regular mallows and kool-aid for flavoring but figured I would try that for another day because I was worried about trying to get the right dilution of koolaid, especially since you need to cut it with water and I knew that wouldn’t get along with the mallows. To make things worse the only koolaid I could find was watermellon-cherry.. Apparently plain old watermellon koolaid is out of style. I brought it into work this morning and sliced it up, so far the reactions are “wow” and “delicious”! Of course, I can barely look at it as I’m the kind of person who is constantly taste testing while I’m making something.. I cut it up this morning and felt my teeth starting to hurt, hah!

  4. Lovely idea! Especially for that someone you dont know what to make for! Consider covering your rice crispy shape in royal icing or white choc ganache before icing – it will give you a firm and smooth surface to adhere your fondant too.


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