Break the toffee into small pieces (I put mine in a freezer bag and bashed at it with a rolling pin), place in a large saucepan with the butter and marshmallows and melt over a low heat. The toffee will try to weld itself to the bottom of your pan, so keep stirring. It will also try to clump together, but stick with it, it takes a bit of time for the last of the toffee to melt and be incorporated but it gets there in the end.
Remove the pan from the heat and stir in the Rice Krispies until they are all well coated in the sticky, sticky mixture
Press into your greased or lined tin and set aside or place in the fridge to cool. Then get your saucepan into the sink to soak asap! I used my 9inch/23cm square tin this time.
Cut into (sticky) squares and have flashbacks to your childhood birthday parties! Or maybe that’s just me…