Recipe | Mint millionaire’s shortbread for Halloween!

Crumbly shortbread topped with mint buttercream and dark chocolate.


I wanted to make mint millionaire’s shortbread and was delighted to find a recipe which also had a Halloween theme with cute white chocolate cobweb decorations. The original recipe for Halloween mint chocolate squares comes from Katie Bryson.

Ingredients (makes approx. 16 slices)

For the shortbread base:

  • 250 g / 8.5 oz plain flour
  • 75 g /  2.5 oz caster sugar
  • 175 g / 6 oz butter (at room temperature so it’s softened)

For the mint layer:

  • 60 g / 2 oz butter (again at room temperature)
  • 2 tbsp milk (I used full fat, but I don’t think it matters which type you use)
  • 2 tbsp custard powder
  • 0.5 tsp peppermint extract (just this little amount makes the buttercream VERY minty. If you’re not a huge fan of mint, you might want to use a little less)
  • 230 g / 8 oz icing sugar
  • green food colouring

For the topping:

  • 200 g / 7 oz dark chocolate (you could use plain or milk chocolate if you prefer)
  • 50 g / 1.5 oz white chocolate


Pre-heat the oven to 180 degrees C (160 fan) / Gas Mark 4 / 350 degrees F. Grease and line your tin. My baking tin measures 20 – 25 cm and is fairly shallow. The original recipe recommends using a 22 x 30 cm swiss roll tin. Obviously a tin with a smaller area will give you thicker layers of shortbread, mint and chocolate.

I used my mixer to combine the sugar, flour and butter, and then finished combining the pastry by hand to rub in the butter the mixer had missed and bring the dough together.

Press the dough into your tin to form a smooth, even layer. Prick all over the dough with a fork.


Bake the shortbread layer for 20 minutes until golden brown. Leave to cool in the tin.


While the shortbread base is cooling, make your mint buttercream. Using your mixer or electric hand beaters, beat the butter until smooth. Then add the milk, custard powder, peppermint extract and icing sugar and continue to mix until you have a smooth buttercream. Add you colouring slowly until you have the shade of green you want. Use a knife (ideally a palette knife) to spread your mint buttercream onto your shortbread base:


Until you have a smooth, even layer:


Put your tin in the fridge for half an hour to get the mint buttercream layer to set.

Melt the dark chocolate either in the microwave (1 minute at first, and then bursts of no more than 30 seconds) or in a bowl over a pan of simmering water. If I made these again, I think I’d use plain or milk chocolate as I find the dark chocolate too bitter. But if you love dark chocolate, you’ll love these!

Pour the chocolate over the mint buttercream layer and use a knife to spread and smooth the surface.


Leave to set, but don’t put in the fridge. If you put it in the fridge, when you slice the shortbread, the chocolate will crack a lot. And look how much it cracks when you allow the chocolate to set at room temp:


The original recipe suggests only scoring out your squares in the tin. I went ahead and cut them. Whatever you think is best!

Melt the white chocolate. Use a piping bag with a small piping tip or cut a very small corner off the corner of your piping bag to pipe a swirl of white chocolate onto each of your mint chocolate squares. Use a cocktail stick or knife to drag lines out from the centre at angles to make web shapes. The following picture shows two rows I’d finished and the bottom row are the swirls before I’d dragged lines through the chocolate.

Baking for Halloween party mint millionaire's shortbread recipe uk green mint chocolate squares

Leave the white chocolate to set, also a room temperature. Lift the whole block of mint chocolate shortbread from the tin using the greaseproof paper (or turn it out if you didn’t use paper). Slice into squares and serve!


And an early Happy Halloween to you all! 🙂

If you’re looking for more shortbread traybake recipes, try:

Millionaire's shortbread featured


Millionaire’s shortbread.





How to make chocolate peanut butter square recipe tray bake no bake


No bake chocolate peanut butter squares.





Claire Huston / Art and Soul



27 thoughts on “Recipe | Mint millionaire’s shortbread for Halloween!

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