In a medium bowl combine the flour, oats, cornstarch, baking soda and salt. Stir to combine, and set aside.

In a large mixing bowl beat the brown sugar, shortening, and oil with an electric mixer until smooth and fluffy. Add the peanut butter and beat until well mixed.

Add the dry ingredients and beat with electric mixer until combined. Using a round 1 tablespoon measuring spoon, scoop out a tablespoon of dough and place on an ungreased baking sheet.

Bake at 375 degrees for 10 minutes. Let cool on baking sheet and then transfer to a baking rack. Mix glaze ingredients together until smooth and creamy and frost each cookie with the peanut butter glaze.