Place flour in a large bowl. Add butter. Using your fingertips, rub butter into flour into fine crumbs form.
Stir in sugar, salt and yolk and stir until a dough forms. Transfer dough to a lightly floured bench. Knead dough briefly until smooth.
Roll dough between sheets of baking paper to form a 23cm round. Mark round into 8 wedges. Prick with fork. Pinch edges of round with fingers to form a decorate edge. Remove top sheet of baking paper. Place dough, on baking paper, on a baking tray.
Bake for 30 minutes. Cool on tray.
Combine jam and approximately 1 tablespoon water in a small bowl (water will vary on brand of jam used - you want a thick, but pourable consistency).
Spoon three-quarters of the jam over biscuit cake. Top with berries and remaining jam mixture. Serve.
Biscuit cake can be cut into wedges along pre-cut markings or broken as desired.
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