Preheat your oven to 180⁰C/Fan 160⁰C/Gas Mark 4 then lightly grease a swiss roll tin (33cm x 22.5cm)
To make the pastry… beat 210g butter and all of the icing sugar together in a bowl, until soft and pale.
Add 1 egg and beat until smooth then fold in the plain flour until the dough comes away from the sides of the bowl.
Flour your work surface then knead the dough until smooth. Shape into a ball then cover in cling film and rest in the refrigerator for 1 hour.
Dust your work surface with flour again then roll out the pastry to 350x250mm. Using a rolling pin lift into the tin then press onto the base and sides gently. Trim off any excess around the top with a sharp knife then return to the refrigerator for 15 minutes to rest.
Spread the jam evenly over the pastry base then set aside.
To make the sponge... Beat the almond extract, caster sugar, self raising flour, baking powder, the remaining butter and eggs all together in a mixing bowl until light and fluffy.
Spoon the batter onto the top of the jam, smooth the surface flat then scatter with the flaked almonds.
Bake in the centre of your preheated oven for 25-30 minutes until well risen and golden (the surface should spring back when pressed).
Transfer to a wire cooling rack to cool completely before slicing into rectangles, then serve and enjoy!