Preheat the oven to 200°C. Grease an 18 inch x 12 inch jelly roll pan and line it with nonstick baking paper. Grease the paper and dust with flour, shaking off any excess.
Blitz the flaked almonds in a food processor to a very fine texture, transfer to a mixing bowl and stir in 110g of the sugar. Beat one egg into the mixture using an electric whisk. After one minute, beat in another egg until the mixture looks pale yellow in colour.
In a separate bowl, whisk the egg whites until they start to froth. Add the remaining 15g of sugar and continue to whisk until the whites look glossy and stiff peaks start to form. Sift the flour into the almond and egg mixture and fold gently together until incorporated. Fold the whites into this mixture in two batches and finish by folding in the melted butter.
Pour into the prepared jelly roll pan and tap gently to remove any air bubbles. Bake in the oven for 12-15 minutes until golden brown. Remove from the oven and cool the whole pan on a wire rack for 10 minutes, before inverting and peeling off the nonstick baking paper.
Cut in half down the middle using a sharp bread knife and arrange one half on a flat baking sheet. Combine the strawberry jam with the diced strawberry in a mixing bowl; it might be quite thick but that is ideal. Spread evenly onto one of the halves of biscuit.
Level using a hot palette knife. Sandwich the other biscuit half on top and press down gently to secure it. Chill for 30 minutes.
Remove and tidy the edges so that they are perfectly even. Cut across the biscuit to make biscuits that are 3-4 cm wide. Arrange on a serving plate.