Step-by-step explanation:
you need to double the recipe and add 1/2, because doubling gets you 48 and adding 1/2 gets you to 60 cookies.
rather than the given recipe, multiply the numbers by 2.5 (double and a half): 2.5c flour
1 2/3 c powdered sugar
1 1/2 c cornstarch
1 7/8 c butter
hope this helps!