Preheat your oven to 180°C (160°C Fan, gas mark 4) and grease a 23cm tart tin with butter or grease. You can also line the base with parchment paper (optional).
Unroll the pre-rolled shortcrust pastry and lay it over the greased tart tin. Gently press the pastry into the base and into the fluted sides of the tin.
With a knife or with your fingers, trim any excess pastry that is hanging over the sides.
Place a layer of parchment paper on top of the pastry and pour baking beans on top. Blind bake the pastry in the oven for 15 minutes then remove the parchment paper and baking beans.
Put the pastry back into the oven and bake for a further 5 to 10 minutes or until the pastry is cooked through.
Once baked, take the pastry out of the oven and set it aside for later use. Be careful when removing from the oven it will be hot.
Add butter, light brown sugar and golden syrup to a large mixing bowl and melt in the microwave on a medium heat.
Stop the microwave every 10 to 15 seconds and stir the mixture thoroughly until melted. You can also melt the ingredients in a pan over a low heat.
Pour cornflakes into the mixture and mix thoroughly until evenly combined.
To assemble the tart, spread jam evenly over the base of the pastry.
Pour the cornflake mixture on top of the jam and spread it out evenly. With the back of a spoon, gently press the cornflake mixture down.
Put the cornflake tart back in the oven for 5 minutes to help it set. Leave to cool down for at least 20 minutes, then serve and enjoy!