Phase 1: Preparing the Shortbread Base

1. Preheat and Prepare Pan: Preheat your oven to 180°C (160°C Fan / 350°F / Gas Mark 4). Grease and line a 20cm x 30cm (8 inch x 12 inch) rectangular baking tin or a 23cm (9 inch) square tin with baking parchment, leaving an overhang on two sides. This overhang will act as handles to lift the slice out easily later.
2. Combine Dry Ingredients for Base: In a large mixing bowl, whisk together the 225g plain flour, 75g caster sugar, and the pinch of salt.
3. Cut in the Butter: Add the 175g cold, cubed unsalted butter to the dry ingredients. Using your fingertips (or a pastry blender or food processor on pulse mode), rub the butter into the flour mixture until it resembles coarse breadcrumbs. Try to work quickly to keep the butter cold.
4. Form the Dough: Bring the mixture together with your hands to form a soft dough. It might seem a little crumbly at first, but it will come together.
5. Press into Pan: Tip the dough into your prepared baking tin. Press it down evenly and firmly across the base using your fingers or the back of a spoon. Ensure it’s level for an even bake.
6. Prick and Pre-bake (Blind Bake): Prick the base all over with a fork. This prevents it from puffing up too much during baking. Bake for 15-20 minutes, or until it’s lightly golden and set. Don’t overbake at this stage, as it will be baked again with the topping.
7. Cool Slightly: Remove the base from the oven and let it cool in the tin for about 10-15 minutes while you prepare the topping. This slight cooling prevents the jam from melting too much and soaking in.

Phase 2: Assembling and Baking the Topping

1. Spread the Jam: Once the base has cooled slightly, carefully spread the 150g raspberry jam evenly over it, leaving a tiny (about ½ cm) border around the edges. This helps prevent the jam from bubbling out and burning.
2. Prepare the Almond Topping:

   • In a separate medium-sized mixing bowl, place the 150g softened unsalted butter and 150g caster sugar. Cream them together using an electric whisk (or a wooden spoon and some elbow grease) until the mixture is pale, light, and fluffy. This step incorporates air, which contributes to a lighter topping.
   • Gradually add the 2 lightly beaten eggs, a little at a time, beating well after each addition. If the mixture looks like it might curdle, add a tablespoon of the ground almonds with the egg.
   • Stir in the 1 teaspoon of almond extract.
   • Gently fold in the 150g ground almonds and the 30g plain flour using a spatula or large metal spoon, until just combined. Be careful not to overmix, as this can make the topping tough.

3. Add Topping to Base: Carefully spoon the almond topping mixture over the jam layer. Spread it out gently and evenly using an offset spatula or the back of a spoon, trying not to disturb the jam layer underneath. Make sure it reaches the edges to seal in the jam.
4. Sprinkle with Flaked Almonds: Scatter the 50g flaked almonds evenly over the top of the almond mixture.
5. Bake to Golden Perfection: Return the tin to the preheated oven (still at 180°C / 160°C Fan / 350°F / Gas Mark 4). Bake for a further 25-35 minutes. The slice is ready when the topping is a deep golden brown, firm to the touch, and a skewer inserted into the centre of the almond topping comes out clean (a few moist crumbs are fine, but not wet batter). The flaked almonds should also be nicely toasted. If the top starts to brown too quickly before it’s cooked through, you can loosely tent it with a piece of aluminium foil for the remainder of the baking time.
6. Cool Completely (Crucial Step!): Once baked, remove the tin from the oven and place it on a wire rack. Here comes the most important part for neat slicing: allow the almond slice to cool completely in the tin. This can take several hours at room temperature, or you can speed it up slightly by placing it in the fridge once it’s mostly cool. Attempting to slice it while warm will result in a crumbly mess. Patience is a virtue here!
7. Slice and Serve: Once completely cool (and preferably chilled for the cleanest cuts), use the baking parchment overhangs to carefully lift the entire slice out of the tin and onto a cutting board. Use a large, sharp knife to cut it into squares or bars. Wipe the knife clean between cuts if necessary for extra neatness.