In the bowl of a mixer or in a large bowl with a hand mixer, cream butter and sugar on medium speed until light and fluffy, 3-4 minutes.
Add vanilla and salt and blend until combined.
With mixer on low, slowly add flour to bowl until well combined. Keep mixer on low and add 5 Tbsp milk in until dough comes together. If cookie dough seems too thick, you can add an additional Tbsp or two of milk (I like my cookie dough firm, so I just use 5 Tbsp).
Fold in M&Ms, candy corn, and peanut butter chips (or whatever candy you choose to use).
Scoop cookie dough into bowls and top with candy eyes if using.