-
1
For the batter: Preheat the oven to 375 degrees F. Line a 12-inch deep dish pizza pan or 10-inch cast-iron skillet with aluminum foil and spray with nonstick cooking spray.
-
2
Whisk the flour, oatmeal, baking soda, salt and cinnamon together in a medium bowl and set aside.
-
3
Beat the butter, brown sugar and granulated sugar with an electric mixer on medium-high speed in a large bowl until well combined, about 2 minutes.
-
4
Add the vanilla and eggs and beat until light in color, 2 to 3 minutes.
-
5
Add the flour mixture and mix on low speed until well incorporated.
-
6
Fold in the chocolate chips by hand using a rubber spatula.
-
7
Press the dough into the prepared pan and arrange 12 to 15 peanut butter cups on the top, pressing flush into the dough.
-
8
Bake until deep golden brown and set, 20 to 25 minutes for the pizza pan or 30 to 35 minutes for the skillet.
-
9
Cool in the pan 10 minutes.
-
10
If removing from the pan, invert the cookie onto a large plate and remove foil, then upright onto a cutting board.
-
11
For the frosting: Beat the butter with the confectioners' sugar, milk and vanilla extract until firm enough to pipe.
-
12
Transfer to a piping bag fitted with a round or star tip.
-
13
When the cookie has cooled, drizzle with melted chocolate if using, then decorate as desired with the frosting and finish with sprinkles.
