Candy Crystals and Chocolate Brownies

Although not strictly a supper, these gluten-free brownies are our absolute favourite and whilst you have the sugar out you can set up a little science activity…growing your own crystals.

Our blue sugar crystals after two days

Science Ingredients

  • Sugar
  • Food colour (optional)
  • Hot water
  • Egg cup
  • Small plate
  • Foil

Supper (sort of) Ingredients

  • Sugar
  • 3 eggs
  • Chocolate
  • Ground almonds
  • Butter
  • Salt
  • Vanilla essence
  • Chocolate chips


  • Line a small traybake/cake tin and pre-heat oven to 170°C
  • Melt 225g chocolate and 225g butter in a bowl (I give it a minute in the microwave, stir and repeat till melted)
  • Leave to cool a little whilst you set up your crystals
    • Cover a small plate with foil
    • Half fill an egg cup with hot water
    • Stir in a tsp sugar and a dash of food colour
    • Put a few spoonfuls of the solution onto the plate
    • Pop on the windowsill, or somewhere it won’t get knocked, for a few days
  • Add 150g ground almonds and 200g sugar to 3 beaten eggs
  • Add a pinch of salt, 2 tsp vanilla essence and combine with the chocolate butter mixture
  • Stir in 200g chocolate chips (yes you read that right)
  • Bake for 25-30 mins and leave to cool in the tin

Science in a Sentence

The water from the plate evaporates into the air as water vapour; sugar molecules are left behind and link together to form crystals (molecules arranged in a regular repeating pattern).


The brownies are more like truffles or very dense chocolate cake, they are devine but not even slightly healthy. You can use any type of sugar; we usually use granulated but it works well with caster and demerara and also with dark, softer sugars although the end result is stickier. Once cooked, we cut these into small cubes and keep half in the fridge and freeze half. They are gluten-free but if you need nut-free or don’t have almonds then you can use rice flour or similar instead. You can also leave out the chocolate chips or substitute chopped nuts, dried fruit or mini-marshmallows.

We use a square brownie tray but have also done these in a round cake tin. If your mixture is less than an inch deep, bake for 15 mins then check and cook a little longer if needed. The end result should be slightly risen with a wobble.

Check your crystals each day, you should see crystals appearing after a day or two. Once the first sugar solution has evaporated, you could carefully add another colour to make a crystal garden.

A warm room will speed up seeing crystals but they will be smaller than a cooler room where the crystals have time to grow as the water slowly evaporates.

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