300g cake flour
1 tsp baking powder
125g salted butter
100g castor sugar
1 Large egg
1 tsp vanilla
Mix together flour and baking powder, then add butter and rub with your fingers until butter is fully incorporated and the mixture resembles breadcrumbs.
Stir in castor sugar.
Whisk together egg, milk and vanilla, then stir into the flour mixture to form a stiff dough.
Remove a third of the dough and place into the freezer to firm up for 10-15 minutes.
Press the remaining 2/3 of the dough into the greased tin.
Spread the jam evenly over the dough, then grate the chilled dough on top of the jam (use the large grate side of the grater).
Bake at 180c for 30-45 minutes or until the top is golden and the jam is bubbling around the edges.
Leave to cool for 20 minutes before slicing, using a serrated knife, into squares.
Store in an airtight container.