Rub the margarine and flour together to form 'breadcrumbs'
Add just enough water to form a soft dough - around 3 tablespoons
Wrap in clingfilm and chill in the fridge for 30 minutes
Preheat the oven to gas 3 / 170C / 340F
Press the dough into the bottom of a lined traybake or swiss roll tin (8"× 12" tin). Prick with a fork
Blind bake for 20 minutes then let cool while you do the next steps - leave the oven on
Melt the sugar, margarine and syrup together in a pan over a low heat
Add the cornflakes and coat in the mixture
Spread an even layer of jam over the base
Pour the cornflake mixture over the tart base and spread out evenly
Bake a further 15 minutes
Let cool fully then cut into squares and serve with warm custard or ice cream
