Place the butter and brown sugar in a saucepan on a medium to high heat.
Once the butter has melted, add the milk and bring to the boil.
Boil for at least 2 minutes before removing from the heat.
Add the salt and allow to cool while you make the slice.
Preheat the oven to 180°C (350°F) and line a 9"x9" baking tin with baking paper.
Beat the butter, brown sugar and sugar together.
Beat in the eggs and vanilla extract.
Beat in the flour, baking soda and cocoa.
Stir in the M&Ms
Pour half into the prepared baking tin and top with the salted caramel sauce. Top with the remaining mixture and top with more M&Ms to decorate and bake for 20 to 25 minutes. The top and sides will be set and a skewer inserted should come out clean.