In the bowl of the stand mixer, cream the butter, sugar, and brown sugar. Add the peanut butter and egg and mix until the peanut butter is thoroughly distributed.
In the medium bowl, stir together the whole wheat pastry flour, oats, baking soda, and salt. Add to the butter mixture and mix until fully combined.
Press the dough into the prepared baking pan with wet fingers. Bake in the preheated oven until golden, about 15 to 20 minutes.
GLAZE: While the dough bakes, mix together the powdered sugar, peanut butter, and milk in the small mixing bowl. Use enough milk to make a glaze with a drizzle consistency.
Remove pan from oven and sprinkle the chocolate chips on top while the cookie base is still hot. The chocolate chips will start to melt and ooze all over the cookie. Drizzle the glaze all over the chocolate layer. Allow to cool before cutting into squares/bars.