Pop popcorn, place popcorn in a bowl and toss the popcorn so the kernels that didn't pop fall to the bottom.
In a large stock pot, melt butter over medium low heat, add in the brown sugar, salt and light corn syrup and whisk until combined. Turn the heat up to medium and bring to a simmer, as soon as bubbles start to form, put a timer on 5 minutes and DO NOT STIR.
When the 5 minutes is up, take off the heat and stir in the baking soda, it will foam you're doing it right! Taking handfuls of the popcorn to make sure you don't get any unpopped kernels, place popcorn into the stock pot and mix to combine. Be extremely careful not to get any of the caramel on your hands IT WILL BURN YOU. When popcorn is as evenly coated as possible, lay it out onto parchment paper in an even layer, squishing it down with a spatula or spoon.
When cool to the touch, break it up into bite sized pieces and place on a baking sheet.
Melt chocolate in the microwave in a microwave safe bowl for 15 second intervals, stirring after each 15 seconds. Drizzle chocolate over popcorn. Place in fridge for about 30 minutes so the chocolate will harden.
In a large bowl, add the chocolate caramel corn with the bag of M&M's®, toss to combine. Serve and enjoy!