In a medium bowl, mix together 150g butter, caster sugar and flour until evenly crumbly. Press into a 23cm (9 in) square baking tin. Bake for 20 minutes.
In a 2 litre saucepan, combine 125g butter, brown sugar, honey and sweetened condensed milk. Bring to the boil, stirring constantly. Continue to boil for 5 minutes. Remove from heat and beat vigorously with a wooden spoon for about 3 minutes. Pour over baked crust (warm or cool). Chill until it begins to firm.
Place chocolate in a microwave-safe bowl. Heat for 1 minute, then stir and continue to heat and stir at 20 second intervals until chocolate is melted and smooth. Pour chocolate over the set caramel layer and spread evenly to cover completely. Chill. Cut into 2 to 3cm squares. These need to be small because they are so rich!