I chose to fill a confetti cake with mini M&Ms. Recipes I've seen online show all sorts of fillings. Reese's Pieces in a chocolate cake with peanut-butter frosting, sparkly sprinkles inside aforementioned Unicorn cake, sour candies or gummi bears in a fruity cake, even wrapped hard candies inside pretty much any flavor. You can do small plastic toys, like party-favor pacifiers for a gender-reveal party. Someone suggested money, but even new coins have tons of germs on them and I'm not even going into what's on paper cash. It's all about the fun of that first slice, when the cake upchucks an extra surprise.
1. Bake a cake. You need a minimum of 3 layers. Most photos I found showed four.
pumpkin cakes out of the freezer and beat the orange and green together. It makes a milk chocolate brown, in case anyone was wondering.
3. I found it easiest to freeze the layers before proceeding. Flip the bottom ring upside-down and put a bit of frosting on it, then upright it and center on a cake circle or final serving plate. Top with filling, then with next cake layer. Repeat if there's a third ring, making sure to put on the filling that will be below the top layer. Crumb coat the open rings and freeze before proceeding.
4. Fill the hole with candy. I got about a cup of mini M&Ms in mine. This will depend entirely upon the size of your cake, size of the hole, and how many layers you used. Fill all the way to the top, and even slightly higher. This needs to support the middle of the top layer of cake. Put the top layer on and finish crumb coating the whole cake. Chill to set crumb coat.
5. Decorate your cake. I had fun with colored sanding sugar on a store-bought white base. You can set a cookie cutter on your cake, fill with a thin layer of sprinkles or colored sugar, and lift. Most of it stays where it's supposed to. For the side sprinkles, I just dried my hands very well and pushed them against the edge.
6. DON'T TELL ANYONE WHAT'S INSIDE! It's so tempting. Do put the cake on a wide cake board or serving platter, maybe with a rim, and place it farther from the edge of the table than you normally would. Depending on the filling, this might get messy.
7. Make sure there's an audience when you cut the cake. This is pretty easy at most parties, but when I do dinner parties I generally show off the cake, then go into the kitchen to hack it apart. People seem under the impression that bakers are good at cutting cakes and pies. Not always.
Difficulty rating :-0