Cut off two triangles of Toblerone and save for later. Roughly chop up the rest of the Toblerone in to bits.
In a pan add the 200g (half a tin) of condensed milk and warm over a gentle low heat for 5 minutes. (strictly no bubbles!)
Add the Toblerone chunks and stir through for another 3-4 minutes.
When melted it will be sticky, at this point add the table spoon of butter to loosen it up slightly. Warm for a further 1 minute until the butter has melted into the mixture.
Pour the mixture into tin lined with greaseproof paper.
Chop up the two Toblerone chunks you saved earlier in to small chunks and crumbs. Sprinkle this over the top of the mixture and gently press it down into the mixture.
Chill for 2 hours and then remove from the tin and cut into your desired bite size pieces.