Gluten-Free Vegan School Cake

Vanilla Lunchbox Tray Bake (Dairy-Free & Nut-Free)

 

If you’re looking for a gluten-free school cake recipe that feels just like the classic vanilla sponge from childhood, this is the one to keep.

 

Soft, light and topped with dairy-free buttercream, this vegan tray bake is:

• 100% plant-based
• Gluten-free
• Egg-free
• Nut-free
• Freezer-friendly
• Perfect for lunchboxes

 

It’s the kind of simple vanilla cake slice that doesn’t feel like a substitute — just a proper piece of cake.

 

Jump to recipe ↓

 

Why We Started Making Our Own School Cake

 

Many schools now offer allergy-friendly options, which is encouraging. But even when meals are labelled vegan or gluten-free, it can still feel uncertain if you’re managing sensitivities at home.

 

 

We noticed that when our daughter was home during the holidays, her eczema would often settle. During term time, flare-ups became more frequent. While it’s impossible to attribute that to one specific factor, reducing school lunches helped bring more consistency.

 

The challenge came on Fridays.

 

Fish and chips were non-negotiable.

 

The main meal was fine — but dessert options were limited. Dry crackers and fruit don’t quite compare to the chocolate cake and custard other children are enjoying.

 

So we agreed she could bring her own dessert.

 

And this vanilla tray bake quickly became the favourite.

 

What Is “School Cake”?

 

 

In the UK, “school cake” usually refers to a simple vanilla sponge baked in a tray, topped with buttercream and sprinkles.

It’s nostalgic.

It’s uncomplicated.

It’s comforting.

 

This version keeps that familiar texture and flavour — but makes it:

• Gluten-free
• Dairy-free
• Egg-free
• Nut-free

Without compromising on softness.

 

Why This Gluten-Free Tray Bake Works

 

Gluten-free sponge can easily become dense or crumbly.

This recipe avoids that by balancing:

• Gluten-free self-raising flour
• Xanthan gum for structure
• Plant-based buttermilk for moisture
• A careful mixing process to develop lightness

 

The result is:

• Soft crumb
• Even rise
• Stable texture for slicing
• Freezer-friendly structure

It behaves like a traditional school tray bake.

 

Why Xanthan Gum Is Essential

Even if your flour blend contains raising agents, xanthan gum is crucial in gluten-free baking.

It:

• Mimics gluten structure
• Prevents crumbling
• Improves sliceability
• Supports freezing and defrosting

Without it, tray bakes can feel fragile.

 

 

 

Lunchbox Cake Slice – Vanilla Tray Bake

Vegan | Gluten-Free | Nut-Free | Egg-Free | Dairy-Free

Yield: Approx. 12 portions

 

Ingredients

Vegan Vanilla Buttermilk Cake

• 165g vegan margarine (melted)
• 120g cane sugar
• 230g self-raising gluten-free flour
• 130g soya vegan buttermilk
• 1/3 tsp baking powder
• 2 tsp cider vinegar
• 1 tsp xanthan gum
• 2 tsp vanilla paste

 

Dairy-Free Buttercream Frosting

• 200g vegan butter
• 400g icing sugar (or erythritol alternative)
• ½ tsp vanilla paste

 

Step 1: Vegan Buttercream Frosting

 

I recommend making the frosting first. It allows you to reuse equipment and break the process into stages.

1. Using a whisk attachment, cream vegan butter for at least 5 - 7 minutes on a fast speed in a stand mixer until pale and smooth.
   This step incorporates air and lightens the colour.
2. Add vanilla paste. Real vanilla gives a beautiful speckled finish.
3. Gradually add icing sugar, one cup at a time.
   Mixing slowly reduces mess and improves texture.
4. Beat for a further 5 minutes.

 

The result should be light, smooth and pipeable.

Store in the fridge for up to one week or freeze for longer storage.

 

Step 2: Vegan Vanilla Buttermilk Cake

 

1. Preheat oven to 180°C.
2. Gently mix melted vegan margarine and sugar until smooth.
3. Slowly add vegan buttermilk and vanilla paste.
   The mixture may look curdled — keep mixing. It will come together.
4. Sift together flour, baking powder and xanthan gum.
5. Fold dry ingredients into wet mixture gently until the batter reaches a smooth dropping consistency.
6. Line a square or rectangular tray with baking paper.
7. Pour batter evenly into the tray.
8. Bake for 25 minutes at 180°C until lightly golden and a skewer comes out clean.
9. Cool in the tin for 5 minutes before transferring to a wire rack.
   Allow to cool completely before frosting.

 

Decorating & Portioning

Once fully cooled:

• Spread or pipe buttercream evenly
• Add sprinkles if desired
• Slice into even squares

For lunchboxes, I recommend slicing before freezing. This makes it easy to remove one portion at a time.

 

Freezing & Storage

This is one of the reasons this gluten-free school cake works so well.

You can:

• Freeze slices individually
• Freeze with buttercream already applied
• Defrost overnight in the fridge or at room temperature

 

The sugar-free frosting option may lose a little structure after defrosting but flavour remains unaffected.

Store in an airtight container for up to 3 days at room temperature.

 

Making It Sugar-Free

You can replace icing sugar with erythritol for a lower-sugar version.

 

Be aware:

• Texture will be slightly different
• Frosting may soften after freezing
• Flavour remains good

If structure is more important than sugar reduction, traditional icing sugar performs better.

 

Why This Recipe Works for Lunchboxes

 

 

This gluten-free vegan school cake is:

• Portable
• Not overly crumbly
• Stable once sliced
• Soft without being sticky
• Suitable for freezing in advance

 

It also feels familiar.

And that familiarity matters when children are navigating food differences.

 

 

Frequently Asked Questions

 

Can I use another plant milk?

Yes — choose one suitable for your household’s sensitivities.

Can I bake this as cupcakes?

Yes. Adjust baking time to 18–20 minutes.

Why does my batter look curdled?

Plant-based buttermilk can temporarily split when added to fat. Continue mixing — it will smooth out.

Can I make this nut-free?

Yes, as long as your chosen margarine and milk are nut-free.

Can I reduce the sugar?

Yes, but reducing sugar too much may affect structure and moisture.

 

Final Thoughts

 

A simple vanilla school cake shouldn’t feel complicated.

 

This gluten-free vegan school cake tray bake keeps everything people love about the original:

• Soft crumb
• Sweet buttercream
• Sliceable texture
• Familiar flavour

 

While making it suitable for gluten-free, dairy-free and nut-free households.

 

It’s freezer-friendly.

It’s lunchbox-ready.

 

And most importantly — it feels inclusive.