DIY Mystery Box Birthday Cake for a Mario-Themed Kids Birthday Party

For my son's 6th birthday, I needed a simple and inexpensive option as I had just returned to work full-time and had my toddler twins in tow. The previous year we had created an epic Mario-Lego themed birthday party at home and left everyone with very high expectations for future years... unattainable expectations now being a full-time working parent! Since he was still very much into Lego and Mario, I knew I wanted to reuse some of those ideas/props but take things offsite and scaled back.

I found a local independent Lego store, Brick Bin, who hosted kids' parties and got started. This shop is amazing - highly recommend for any local Lego-parents as you can purchase bricks in bulk and find one-off pieces that may go missing from pre-purchased sets. The best part was their team hosted the party, provided decor, plates and cutlery and all we had to do was supply the food. They even provided goodie bags and build-your-own minifigure giveaways for the kids!

Since this party was in the morning (10am-12pm), I only needed minimal snacks and a birthday cake - so I knew the cake needed to be the focal point of my DIY efforts this year. After some Pinterest scrolling, I decided a mystery box DIY birthday cake was the way to go since it seemed somewhat simple. My son and I always watched those baking competition shows and recently we had watched a challenge where they had to have a surprise reveal in the center of the cake. I knew that we could use the concept of the punch boxes and chocolate coins from his last party as the surprise!

Mystery box DIY birthday cake with chocolate coin surprise center

I am NOT a baker, so boxed cake was the way to go. If you haven't heard of the box cake hack, definitely look that up online (essentially you just replace the oil with butter and add extra eggs). This takes a box cake to the next level by making it taste homemade. Of course, my son requested both chocolate and vanilla, so that added another layer of complexity, however since it was a square cake, it was easy enough to bake multiple flavors.

I used an 8x8 square cake pan and did two layers of each flavor with a butter cream icing between each and around the edges. Again, I am not a baker, so this post is meant for inspiration only. I used a knife to cut a hole in the middle two layers but left the top and bottom whole. I also assembled the cake on the lid of a large plastic tub (from Dollarama) for easy transport. Before I put on the top layer of cake, I filled the hole with chocolate coins for the surprise reveal.

The outer layer of frosting was definitely a challenge. I would recommend chilling the cake before doing that part as the chocolate cake started flaking into my yellow frosting. I used white chocolate chips and white candy melts to add the question mark details on the sides and top of the cake for a simple decoration (again, keeping it easy and fool-proof).

The kids were so excited to see the coins fall out of the cake when I cut through it. Definitely a core memory. I hope this provides some inspiration for a cake or party for your littles in the future. Enjoy!

xo Liss