Prepare the biscuits: Break the tea biscuits into bite-sized pieces by hand or gently crush them with a rolling pin, leaving some larger chunks for texture.

Melt chocolate: In a heatproof bowl over simmering water (double boiler), melt 6 ounces of dark chocolate until smooth. Set aside to cool slightly.

Cream butter and sugar: In a large bowl, beat the butter and caster sugar together until light and fluffy.

Combine ingredients: Stir the melted chocolate into the butter and sugar mixture until fully combined.

Add biscuits: Fold the broken biscuits gently into the chocolate mixture, ensuring all pieces are coated.

Shape the cake: Line a loaf tin or round cake tin with parchment paper. Press the mixture firmly into the tin, smoothing the top with the back of a spoon.

Add chocolate topping: Melt the remaining 8 ounces of dark chocolate and pour it evenly over the pressed biscuit mixture. Spread gently to cover.

Add garnish: Sprinkle mini chocolate chips, sprinkles, or curls on top for decoration, if desired.

Chill: Refrigerate the cake for at least 4 hours, preferably overnight, until firm and set.

Serve: Slice into thick slices and enjoy as a decadent treat with tea or coffee.