Whisk together all of the ingredients in a small pan until smooth, place over a medium heat and whisk constantly until in comes to a boil; cook for one minute (while whisking) then remove from the heat and allow to cool. Chill in the refrigerator before using.

In a mixing bowl, stir together the melted butter and the sugar until smooth then mix in the flour, salt and vanilla extract followed by the M&M's.

Form the dough into a disc about 1cm thick, wrap in clingfilm and refrigerate until firm. Once chilled, either chop the disc into bitesized pieces or break bits off and roll into small balls. Store the cookie dough pieces in the freezer until ready to use.

In a large bowl, whisk the cream until soft peaks form then gently fold in the condensed milk and vanilla extract.

Drizzle some of the chilled chocolate fudge sauce over the base of a large freezer-proof container, dollop over about a third of the ice cream base, scatter over some of the cookie dough pieces and drizzle over some more fudge sauce. Repeat the layering until you have used all of the ice cream base and the cookie dough, you may not need all of the fudge sauce.

Freeze the ice cream overnight until firm.