01 -
Melt 1 1/4 cups butter completely. Mix the melted butter with quick oats, all-purpose flour, and brown sugar. Press two-thirds of the mixture into a greased or parchment-lined 9x13 inch pan. Bake at 325ºF for 10 minutes, then allow it to cool. Set aside the remaining one-third of the crust mixture for topping.
02 -
Melt 1/4 cup butter in a saucepan over medium heat. Stir in brown sugar until smooth, about 1 minute. Add milk, vanilla extract, and flour one at a time while stirring continuously. Bring the mixture to a slow boil and cook for about 3 minutes until it begins to thicken. Stir continuously, then remove from heat.
03 -
When the crust is cool to the touch, pour the caramel filling evenly over it. Sprinkle the reserved crust mixture over the top. Bake at 300ºF for an additional 20 minutes. The bars may appear runny but will firm up as they cool completely.