Crush biscuits for 2 Seconds, speed 4-6 and set aside.
Use turbo to crush clinkers until they are broken up, but not too small, as you want to see the colours in the slice. Set aside with the biscuits.
Add butter and condensed milk to thermomix bowl for 2 minutes, 60 degrees on speed 2.
Add the biscuits and clinkers to TM bowl on reverse, speed 4 until mix is combined.
Put mix into slice tin and press flat. Clean thermomix bowl and dry to ensure no water remains.
When mix is cool, melt chocolate in TM bowl for 2 minutes, 50 degrees on speed 3. Pour over the clinker base and place into fridge until set. Cut into squares and enjoy.