To create the peanut butter oatmeal bars, start by mixing together the butter and sugars using a hand or stand mixer, then add in the egg, peanut butter, salt, and vanilla. After that fold in the flour and oats by hand and press the mixture into an 8x8 baking dish that has been lined with parchment paper or sprayed with cooking spray. I highly recommend using parchment paper for easy cutting of the bars. Next you're going to create your peanut butter streusel using brown sugar, flour, peanut butter, and butter. Mix together well until a crumbly consistency forms, then sprinkle on top of the peanut butter oatmeal bars. Place the bars in a 350 degree preheated oven and bake for 25-28 minutes, or until the bars are lightly golden. While the bars are baking, mix together your peanut butter drizzle using powdered sugar, peanut butter, and milk. Although the recipe calls for 2-4 tsp, note that you may have to add more or less milk depending on the weather and other variables. Add 1 tsp at a time and continue adding as needed until a light drizzle is reached.