Immediately remove from heat: Dot with remaining 2T of butter and let cool to lukewarm (about 110º) without stirring.
Add vanilla and beat vigorously until fudge becomes thick and begins to lose it’s gloss. An immersion blender is a wonderful tool for speeding this process up, but a fork works just fine too. At this point, you can add chopped pecans.
Quickly spread fudge into buttered shallow pan – I use a 9×5 bread pan for this size recipe.