Make the pretzel ice cream: Prepare an ice bath in the sink or in a large heatproof bowl.
In a large saucepan, heat the milk over medium-high heat until it starts to steam, about 5-10 minutes. Remove the pan from the heat and stir in the pretzels. Cover the pan and let the pretzels steep for 20 minutes.
Pour the mixture through a wire-mesh strainer into a bowl, pressing down on the pretzels to extract as much milk as possible. Don’t worry if some of the pretzel “pulp” pushes through into the ice cream. That’s totally OK. Return the pretzel-infused milk to the saucepan.
Add the sugar and skim milk powder. Stir with a hand mixer or whisk until smooth. Make sure the skim milk powder is wholly dissolved into the mixture and that no lumps remain (any remaining sugar granules will dissolve over the heat). Stir in the cream.
Clip a candy thermometer to the saucepan and set the pan over medium heat. Cook, stirring often with a rubber spatula and scraping the bottom of the pan to prevent sticking and burning, until the mixture reaches 110ºF, 5 to 10 minutes. Remove the pan from the heat.
Place the egg yolks in a medium bowl. While whisking, slowly pour ½ cup of the hot milk mixture into the egg yolks to temper them. Continue to whisk slowly until the mixture is an even color and consistency, then whisk the egg-yolk mixture back into the remaining milk mixture.
Return the pan to the stovetop over medium heat and continue cooking the mixture, stirring often, until it reaches 165ºF, 5 to 10 minutes more.
Transfer the pan to the prepared ice bath and let cool for 15 to 20 minutes, stirring occasionally. Pour the ice cream base through a wire-mesh strainer into a storage container and place in the refrigerator for 1 to 2 hours, or until completely cool.
Make the munchies mix-in: Preheat the oven to 275ºF. Butter a 12-by-18-inch baking sheet and line it with parchment paper.
In a large bowl, using your hands, break up the crackers, pretzels, and potato chips into pieces about a quarter of their original size. The goal here isn’t to pulverize them into dust (though a little dust is OK, as it will help bind everything together later on). Add the skim milk powder and sugar and toss to combine. Pour the butter over the mixture and work it together with your hands, squeezing it into clumps and breaking it apart, almost like kneading dough.
Spread the mixture evenly over the prepared baking sheet and bake for 20 minutes, until the mixture just begins to toast and turn brown. Set aside to cool completely.
Transfer the cooled base to an ice cream maker and churn it according to the manufacturer’s instructions.
Transfer the ice cream to a storage container, folding in the munchies mix-in and M&M’s as you do. Use as much of the mix-in as you want; you won’t necessarily need the whole batch. Serve immediately or harden in your freezer for 8 to 12 hours for a more scoopable ice cream.
The Munchies Ice Cream was originally written by Leigh Anne Wilkes at https://www.yourhomebasedmom.com/the-munchies-ice-cream/.