Put the flour in a microwave-safe bowl and microwave on high until the flour reaches a temperature of 180 degrees F, 1 to 1 1/2 minutes. Whisk to get rid of as many lumps as you can. Set it aside to cool.
In a stand mixer fitted with a paddle attachment, combine the peanut butter, brown sugar, sugar, butter, heavy cream, vanilla and salt and mix on medium-high, scraping down the sides of the bowl periodically with a rubber spatula to ensure that everything gets combined, until light and fluffy, 3 to 4 minutes. Add the flour and oats and mix to combine. Add the M&M's and mix to combine. Store by the scoop or in balls in the fridge in an airtight container for up to a week.