Method

1. Line a 20cm square tin with baking parchment. Melt the marshmallows and butter together in a large saucepan over a medium heat, stirring continuously until completely smooth. Stir in the vanilla extract.

2. Tip in the cereal and stir quickly using a silicone spatula until fully coated in the marshmallow mixture. Working quickly before it starts to set, scrape the mixture into the prepared tin and press it firmly into an even layer using the back of a spoon or the spatula. Chill for at least 1 hr until firm.

3. Melt the white chocolate in a heatproof bowl in short bursts in the microwave, stirring between each, or over a pan of simmering water, ensuring the bowl doesn’t touch the water. Stir until smooth.

4. Divide the melted chocolate between four small bowls. Leave one bowl white, then colour the remaining three bowls pink, blue and purple (or the colours of your choice). Alternately spoon the different chocolate colours over the chilled rice crispy layer, then dot over a little extra food colouring, if you like, for a more dramatic galaxy effect. Gently swirl the colours together using a skewer or knife – don’t go too far, or the colours will blur together. Scatter over the sprinkles, then chill for 30 mins, or until the chocolate has set. Cut into 16 squares to serve. Will keep in an airtight container for three days.