Gigantic choc-marshmallow cookie sandwiches

Preheat oven to 180°C fan-forced (200°C conventional). Grease a 23cm round fluted silicone pan with cooking oil. Put pan on an oven tray large enough to sit level.

Put butter, sugar and egg in a large bowl. Using a hand whisk, mix until combined. Sift in flours and stir until a soft dough forms. Divide dough in half.

Press 1 dough portion firmly into prepared pan and smooth surface. Wrap remaining dough in plastic wrap and set aside. Put pan in oven for 20 minutes or until light golden. Remove from oven, set aside for 15 minutes to cool then put in fridge for 30 minutes or until cold. Turn out biscuit onto a wire rack, decorative side up.

Wash and dry pan thoroughly then regrease. Press remaining dough into pan and smooth. Bake for 20 minutes. Remove from oven and spread 1⁄2 of the jam over warm biscuit, leaving a 5mm border. Cover jam with a single layer of marshmallows, starting from centre and working around in circles until you reach edge of jam. Bake for a further 5 minutes or until softened.

Meanwhile, spread remaining jam onto smooth side of cooled biscuit.

With marshmallow biscuit still in pan, immediately sandwich  with other biscuit, jam-side down. Gently but firmly push down to squash marshmallows and level. Chill for 1 hour then remove biscuit sandwich from pan. Wash and dry pan thoroughly.

Melt chocolate and extra butter in a medium heatproof bowl set over a saucepan of gently simmering water then set aside for 5 minutes to cool.

Spoon chocolate mixture into pan, spreading with a spoon to cover base. Carefully put biscuit sandwich back into pan on top of melted chocolate and gently but firmly push down to level surface. Chill for 2 hours to set.

Turn out biscuit sandwich onto a chopping board, chocolate-side up. Set aside for 5 minutes then cut into pieces using a large knife. Serve.

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