Line an 8” square baking dish with parchment paper.
Heat flour in 10-second increments and stir between until it reaches 160 degrees and set aside (it took mine 4, 10-second increments).
Combine almond bark, sweetened condensed milk, unsalted butter, brown sugar, and salt in a double boiler.
Heat on medium/low heat until smooth.
Once smooth, reduce to low heat and stir in flour until combined.
Remove from heat and stir in vanilla.
Let cool for 3 minutes and add 1/4 cup of M&Ms to the batter.
Pour batter into the prepared pan and add the remaining M&Ms to the top.
Let the fudge cool for 6-8 hours or overnight until hard.