Thomas the Train Smash Cake

Thomas the Train Smash Cake with Homemade Marshmallow Fondant decorations and vanilla buttercream for a special little boy’s 1st birthday party!

Thomas the Train Smash Cake

My very good friends Jenny and Jeff recently threw a party for their son Andrew’s 1st birthday. I was honored when she asked if I would make his cake. After making the Monkey Face Sugar Cookies with Royal Icing for her baby shower last year, I wanted this cake to be very special for such a big occasion.

We decided that I would make a small cake for him to get into and cupcakes for the rest of the guests. Jenny went with a train theme for the party – she decorated the tables with red table clothes and used black streamers to make “train tracks” down the length of each table. Andrew wore a shirt featuring a train and a big “1.” There were pictures up around the room of Andrew from each month of his life. It’s amazing to see how much he’s grown!  

Thomas the Train Smash Cake

Like most babies, Andrew had never had many sweets before. He was timid at first but then enjoyed running his tiny hands over the surface of the blue buttercream frosting. He particularly liked the fondant decorations, which was surprising and a little worrisome given their chewy/gum-like texture, so we gently encouraged him to focus more on the frosting.

When he got his first real taste of the buttercream, his little legs started shaking up and down – seriously the cutest thing! Andrew seemed to enjoy his cake, and his guests really liked the cupcakes. The party was so much fun for everyone, and I hope Andrew will look at pictures and the video someday and be so proud that his parents put forth the effort for his 1st birthday . . . or at least Jenny and Jeff will have happy memories of this major milestone in the life of their first child! 🙂  

Smash Cake Details

I decided to cheat and used a box mix for the cake and cupcakes for 3 reasons, 1) the amount of cake batter I needed for 36 cupcakes and a 6″ double layer cake, 2) the party was on a Saturday meaning everything had to be made on weeknights after I got home from work, and 3) cake mixes are just so darn moist and stay that way even when the cupcakes are refrigerated for a few days.  

I used 2 boxes of Duncan Hines yellow cake mix (the only brand my aunt, who is the designated birthday cake baker in our family, uses). This made 36 cupcakes and 2-6″ layers. I also made a double batch of Easy Vanilla Buttercream. The cupcakes were frosted with buttercream, and these adorable toothpick toppers that Jenny made were inserted at the party:  

cupcake with a 1 pick in it

The buttercream was used to bind the 2 layers and coat the entire cake. I piped more buttercream around the top and bottom of the cake using a large star tip (I believe it’s a Wilton 1M). Then I set out to conquer fondant.  

I have been wanting to try Annie’s recipe for Marshmallow Fondant for a while now, and I used her Fun with Fondant tips as a guide. I cut the recipe in half and still had much more than enough for making the decorations. I used an X-acto knife and free-handed the decorations. I just added a little more buttercream to the back of each before “pasting” them to the cake – not sure if it was necessary but I wanted to make sure they would stick.  

Thomas the Train Smash Cake

I used store-bought black gel icing to draw a train track around the cake, and Jenny found a “Thomas the Train” toy that we put on the track at the party. Coincidently, she discovered that all Thomas the Train’s have a “1” on them – perfect for a 1st birthday party!!!  

I think that’s it! I consider my first run at fondant a success, and I’m exciting to use it again.  UPDATE: Check out the Bridal Shower Cake I made for my sister using Marshmallow Fondant!

Thomas the Train Smash Cake Pin

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Thomas the Train Smash Cake

Thomas the Train Smash Cake

This Thomas the Train Smash Cake is decorated with Easy Vanilla Buttercream and homemade Marshmallow Fondant.
5 from 9 votes
Prep Time 55 minutes
Cook Time 5 minutes
Rest Time: 2 hours
Total Time 3 hours
Course Dessert
Cuisine American
Servings 6


For the Marshmallow Fondant:

  • vegetable shortening (for greasing bowls)
  • 8 ounces plain marshmallows (1/2 bag)
  • 1 tablespoon water
  • 1 teaspoon clear flavoring (such as vanilla extract)
  • 1 pound powdered sugar (divided)
  • pinch of salt

For the Cake:

  • 1 box cake mix of your choice (prepared and baked in 2 or 3 6-inch layers)
  • 1 batch Easy Vanilla Buttercream (see note)

For Decorating:

  • blue, red and black food coloring gel
  • black gel icing (for drawing train track)


Make the Marshmallow Fondant:

  • Using the shortening, generously grease a large microwave-safe bowl, the bowl of the stand mixer, a spoon/spatula (or two), and the mixer dough hook.
  • Add the marshmallows and water to the prepared microwave-safe bowl and microwave for 60 seconds. Stir with the greased spatula/spoon. If not all the marshmallows have melted, microwave for 30 more seconds. Stir in the flavoring.
  • Reserve 1/2 cup of the confectioners’ sugar and add the rest to the bowl of the stand mixer, along with the salt. Create a well in the center. Pour the marshmallow mixture into the well and turn the mixer on to the lowest setting. When the mixer sounds strained, turn the speed up one setting. Turn off the mixer once all the sugar has been incorporated. If the fondant is sticky, add the reserved sugar 2 tablespoons at a time until it is no longer sticky. You may not need any.
  • Turn the fondant out onto a piece of plastic wrap. Rub a bit of shortening on the outside of the ball. Wrap tightly with the plastic wrap, place it in a resealable plastic bag and let rest for at least 2-3 hours. Keep the unused portions covered when not in use. If the fondant becomes stiff, microwave for 20 seconds at a time until it becomes pliable.

Assemble the Cake:

  • Cover a cake board or platter with aluminum foil.
  • Place a small amount of buttercream in the center of the cake board and place 1 layer of cake on top. Cover layer with buttercream and add another layer of cake. Repeat for all cake layers and cover cake with a thin crumb coat. Refrigerate for 15 minutes.
  • While the crumb coat sets, color portions of the fondant dark blue, red and gray. Roll the fondant out and use a sharp knife to cut out train, wheels, and a "1" shape. You will likely need 3 train shapes, 6 smaller wheels, 3 larger wheels, and 4 "1" shapes.
    Thomas the Train Smash Cake
  • Tint buttercream with blue food coloring gel to a medium blue. Tint a small amount of buttercream to dark blue for the lettering.
  • Frost the outside of the entire cake with the medium blue frosting. Apply the train, wheels, and 1's around the cake and place the last "1" on top of the cake.
  • Fill a pastry bag with a small round tip and pipe the lettering on top with the dark blue buttercream.
  • Fill a pastry bag with a small star tip and pipe a border around the top and bottom edges of the cake.
  • To finish, pipe a train track around the cake on the cake plate with the black gel icing.


Marshmallow Fondant recipe is a half batch 
Fondant Source: Adapted from Annie’s Eats
Easy Vanilla Buttercream recipe
You’re Gonna Bake It After All
Keyword American, cake, dessert, party

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