With 2/3 of a cup of butter, you cannot make any mini pies as you have insufficient butter.
To determine the number of mini pies you can make with 2/3 of a cup of butter, divide the available butter (2/3 cup) by the butter required per pie (3/3 cup) to find the number of pies possible.
Number of pies = Available butter / Butter per pie
Number of pies = (2/3 cup) / (3/3 cup/pie)
Number of pies = 0.6666 pies
Since you cannot make a fraction of a pie, round down to the nearest whole number. Therefore, you can make 0 mini pies with 2/3 of a cup of butter.