1. Heat oven to 375°F.
2. Make chocolate chip cookie dough as directed on pouch. Use 1 tablespoon to measure 24 balls of dough. Arrange balls 2 inches apart on 2 ungreased cookie sheets.
3. Bake 8 to 10 minutes or until set around edges. Cool on cooling rack.
4. Spray 13x9-inch (3-quart) baking dish with cooking spray. Make oatmeal cookie dough as directed on pouch; press dough into baking dish.
5. Bake about 15 minutes or until set around edges. Cool completely, about 30 minutes.
6. In medium bowl, beat butter, powdered sugar, cream and vanilla with electric mixer on medium speed until light and fluffy.
7. Cut half of the oatmeal cookie into small pieces, or crumble. (Reserve remaining oatmeal cookie for another use.)
8. Add crumbled cookie to frosting.
9. Mix completely.
10. Spread about 1/4 cup oatmeal cookie frosting between bottoms of 2 chocolate chip cookies, sandwiching them together. Repeat to make 12 cookie sandwiches.