Preheat the oven to 220C (200C fan-assisted / 430F).
Sift the flour and icing sugar into a mixing bowl.
Cube the butter and rither rub together with the flour and icing sugar by hand in a bowl or pulse in the food processor until fully combined.
Add the cold water, then either pulse in the food processor, or mix through with a round knife until it comes together.
Knead the pastry a couple of times so it comes together in a smooth ball. If it’s very soft, wrap and chill in the fridge until firm enough to work with.
Roll out on a lightly floured board to create a rectangle 5cm (2 inches) wider and longer than the base of the tin.
Lightly grease the tin, then line with the pastry so it comes up the sides a bit. Trim to neaten, if necessary.
Prick all over with a fork. Chill in the fridge for 5-15 minutes or until firm to the touch.
Cover with greaseproof and baking beans, then bake blind for 15 minutes (this stage is what helps ensure the pastry is cooked and not soggy at the end) until just slightly taking on colour.
Remove the paper and beans and leave to cool for 10 minutes.
Turn the oven down to 180C (160C fan-assisted / 350F).
To make the raspberry layer
Stir the raspberry jam to loosen, then spread on top of the pastry up to the edges.
Dot the raspberries on top, so they are fairly evenly spaced.
To make the sponge
Reduce the oven temperature to 180C (160C fan-assisted / 350F).
Put the sugar and butter in a bowl and beat together until very pale and fluffy.
Whisk in the eggs, milk, vanilla and almond extract.
Fold in the flour and ground almonds until combined into a thick batter.
Spoon in dollops into the tin so that you don't disturb the raspberry layer. Gently level off.
Top with the flaked almonds, scattered evenly
Bake in the middle of the oven for 1 hour - 1 hour 15 minutes, or until it's firm in the middle.
Cool in the tin on a wire rack
To finish
Once completely cool, run a palette knife or cutlery knife around the edges of the tin to loosen, then turn the bake out and place on a board.
Mix together the jam and boiling water together in a small dish until smooth, then brush all over the top of the cake. Allow to sink in for a few minutes.
Use a very sharp knife to slice carefully into 12-16 equal pieces.
Video
Notes
Store any remaining slices in a sealed container in a cool place. They should keep for 3-5 days.