Microwave Bento Cake (No Cake Tin Needed!)

Name: Microwave Bento Cake (No Cake Tin Needed!)
Prep time: 10 min
Cook time: 2 min
Ingredients: 6 tbsp all-purpose flour; 3 tbsp granulated sugar; ½ tsp baking powder; Pinch of salt; 4 tbsp milk (dairy or plant-based); 1 tbsp melted butter or neutral oil; ½ tsp vanilla extract; Vegan? Use plant-based milk and oil.; ¼ cup 60g unsalted butter (or vegan butter), softened; ½ cup 60g powdered sugar; ½ tsp milk or cream; ¼ tsp vanilla extract

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Serves: 1–2
Prep Time: 10 minutes
Cook Time: 2–3 minutes
Cool + Decorate Time: 15–20 minutes
Total Time: ~30 minutes
Vegan Option Included

What This Is

Bento cakes – also known as lunchbox cakes – are the adorable, miniature layer cakes taking over Instagram and TikTok feeds. Typically around four inches wide, these compact confections are frosted like full-sized celebration cakes but designed for just one or two people to enjoy. They’re cute, customizable, and often tucked into takeaway-style boxes with pastel frosting, piped borders, and short, sweet messages like “You got this” or “Happy Mini Cake Day.” It’s easy to see why they’ve gone viral: they’re part dessert, part self-care ritual, and totally Instagrammable.

But while most bento cakes require baking and special pans, this microwave version makes the trend more accessible than ever! No oven, no cake tins, just a quick and easy method to create your own beautifully frosted, single-serving cake in under 30 minutes. Whether you’re celebrating something small or just treating yourself, this recipe delivers all the bento cake charm with none of the fuss.

Ingredients

For the Sponge Cake

6 tbsp all-purpose flour
3 tbsp granulated sugar
½ tsp baking powder
Pinch of salt
4 tbsp milk (dairy or plant-based)
1 tbsp melted butter or neutral oil
½ tsp vanilla extract

Vegan? Use plant-based milk and oil.

For the Frosting (Bento Cake Buttercream)

¼ cup (60g) unsalted butter (or vegan butter), softened
½ cup (60g) powdered sugar
½ tsp milk or cream
¼ tsp vanilla extract
Optional: food coloring, sprinkles, piping bag or ziplock bag

What to Use Instead of a Cake Tin

Use any of the following microwave-safe options that hold about 8–10 oz (240–300ml) of batter:

A 4-inch ramekin (tall sides ideal)
A microwave-safe takeaway container (round or square)
A small glass prep bowl
A ceramic soup bowl or pyrex measuring cup

Avoid metal or anything with metallic trim in the microwave.

Line the base with a small round of parchment paper (optional, but helps with release) and grease the sides lightly with butter or spray.

Method

Step 1: Mix the Cake Batter

In a small bowl, mix flour, sugar, salt, and baking powder.
Add milk, melted butter or oil, and vanilla. Stir until smooth and lump-free.
Pour into your greased microwave-safe container, leaving some room at the top (it will rise!).

Step 2: Microwave the Cake

Microwave on high power for 2 minutes.
Check: insert a toothpick in the center. If it comes out wet, microwave in 10–15 second bursts until just cooked (usually 2.5 to 3 minutes total).
Let cool in the container for 5 minutes, then turn out onto a plate and cool completely.

Don’t overheat, microwave cakes can dry out quickly. Stop cooking as soon as it’s set and springy to touch.

Step 3: Level & Layer

Slice off the domed top with a serrated knife to make it flat.
If your cake is tall enough, slice it in half horizontally to create two layers.

Optional: Trim the edges with a round glass or cutter to make a clean bento-style round cake (about 4 inches wide).

Step 4: Make the Frosting

Beat the softened butter until smooth.
Gradually mix in powdered sugar and beat until fluffy.
Add milk and vanilla, adjusting for consistency.
Tint with a drop of food coloring for pastel tones (optional).

Step 5: Decorate Bento-Style!

Apply a thin crumb coat, chill for 5 minutes.
Smooth a second layer of buttercream over the top and sides.
Pipe a border around the top using a ziplock or piping bag.
Add sprinkles or write a tiny message like:
- “Happy Mini Cake Day”
- “You Got This”
- “Sweetest Moment”