How to Make Lego Birthday Cakes

Updated March 23, 2017

According Lego, children around the globe spend 5 billion hours each year playing with Lego building blocks. As parents, we remember playing with Lego toys just as our children enjoy these classic building blocks today. With a little bit of cake batter, marshmallows, frosting and food colouring, you can create an appealing Lego birthday cake for your child's birthday. In fact, Lego bricks can be your party theme. Try building a Lego centrepiece, giving small Lego toy sets to party guests and creating Lego inspired games such as guessing the number of Lego bricks in a jar.

Bake a 9-by-13 inch sheet cake, following the directions on the cake mix box or using your own recipe.

Once your Lego birthday cake is finished baking, allow it to cool for 15 minutes in the pan. Place the cake on a cooling rack for one hour to cool completely.

Place the cake on a tray. Cut your Lego birthday cake into three rectangular pieces using a serrated knife. Cut one rectangular piece in half to make two smaller squares.

Cover the four Lego birthday cake pieces loosely with a dish towel. Place the cake in your freezer until it is firm. This should take no more than one hour. Remove one piece to frost. Leave the other pieces in the freezer, taking them out one at a time as you are ready to frost them.

Cut 12 large marshmallows in half horizontally creating 24 round marshmallows that are half as tall as they started out being. The marshmallows are the knobs on the Lego bricks.

Mix vanilla frosting and one colour of paste food colouring in a bowl. Start with a larger piece of cake. Frost the cake spreading the frosting evenly on the top and sides of the cake.

Place the marshmallow on a fork. Frost the marshmallow. Set the marshmallow on the cake.

Place eight frosted marshmallows, two by two, on the top of the two rectangular pieces of cake. Place four frosted marshmallows, two by two on the top of the two square pieces of cake. Copy the pattern of knobs on a Lego brick.

Repeat Step 2 and Step 3 for the remaining rectangular piece and the two smaller square pieces of your Lego birthday cake. For each separate cake piece with its marshmallow knobs use a different colour. This will give you four different colour Lego birthday cake bricks.

Place the Lego birthday cake bricks on a serving tray or aluminium-covered card board cut outs. Store the cake at room temperature.


This Lego birthday cake will feed 12 to 16 people and will take approximately three to four hours to complete.

Things You'll Need

  • Cake mix
  • Eggs
  • Vegetable oil
  • Water
  • Vanilla frosting
  • Paste food colour (red, blue, green and yellow)
  • 12 large marshmallows
  • Baking spray with flour
  • Bowls
  • Measuring Cup
  • Mixing spoons and fork
  • 13-by-9 inch sheet cake baking pan
  • Oven
  • Cooling rack
  • Tray
  • Serrated knife
  • Dish towel
  • Freezer
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About the Author

Ashlyn Etree was all business as a PR professional for 10 years, but she loves rolling up her sleeves volunteering at animal rescues. She writes for various publications, specializing in business, career and pet-related content. Etree earned a Bachelor of Arts in communications from the University of Central Florida.