If you are using a stand mixer, add about 20 pieces of the candy you have chosen (mini peanut butter cups, M&M's add 1/4 cup) and mix until they are broken chunks are throughout the batter. (No need to chop them, the mixer does the work for you.) If you’re using a hand mixer, you should rough chop the candies by hand to mix them in easier. Mix the candy in the batter until incorporated.
Coarsely chop remaining candy.