Step 1

Heat oven to 375°F. In large bowl, stir cookie mix, graham cracker crumbs and melted butter until a soft dough forms. Press dough evenly into ungreased 8- or 9-inch square metal pan.

Step 2

Bake 20 to 25 minutes or until dough is set and golden brown. Cool completely, about 30 minutes.

Step 3

In 2-quart saucepan, heat chocolate chips and condensed milk over medium-low heat 10 minutes, stirring frequently, until chips are melted and mixture is thickened. Spread evenly over cooled cookie crust. Refrigerate 30 minutes or until set.

Step 4

Set oven control to broil. Sprinkle marshmallows evenly over chilled fudge filling. Broil 1 minute, rotating pan as needed until marshmallows are melted and lightly toasted. Refrigerate at least 1 hour before cutting into bars.

Step 5

For 16 bars, cut into 4 rows by 4 rows; for 20 bars, cut into 5 rows by 4 rows.