Add the cornflakes to a ziploc bag and use a rolling pin to crush them into pieces smaller than a pea. You want crunchy bits, not dust. Set aside.
In a microwave-safe bowl, melt the butterscotch chips, peanut butter, and corn syrup in 30-second intervals. Stir between each heating until all the butterscotch chips have melted.
Stir the crushed cornflakes into the peanut butter mixture until combined. The mixture should be very thick and easily stick together, add additional crushed cornflakes if needed to reach the right consistency.
Line a baking sheet or plate with wax paper. Using a cookie scoop, portion some of the cornflake mixture into the palm of your hand and roll it into a 1-inch to 1.5-inch ball. Place the ball into the wax paper. Repeat until all of the cornflake mixture is rolled. Place the truffles into the freezer for 1 hour.
After 1 hour, pour the semi-sweet chocolate chips into a microwave-safe bowl. Melt them in the microwave in 30-second intervals, stirring between each heating, until melted. (see note) Let the chocolate sit for a few minutes to cool down.
Remove the truffles from the freezer. Dip each truffle into the melted chocolate, coating it completely, before setting it back onto the wax paper. Let the truffles sit until the chocolate has hardened.
Roll the truffles in powdered sugar until coated, knocking off any excess sugar as needed. Serve immediately or store in an airtight container in the refrigerator.
Notes
If the melted chocolate is too thick, add 1 tablespoon of coconut or vegetable oil and heat for another 30 seconds until melted. Then stir everything together. You can also do this if the chocolate starts to set up while you're dipping the cold truffles.