1. Preheat oven to 350ºF and coat a 15×10″ jelly roll pan with cooking spray. Set aside.
2. In a large bowl mix 1 c. of unsalted butter, all-purpose flour, rice flour and granulated sugar with a wooden spoon until well combined and a little crumbly. Press dough in an even thin layer onto jelly roll pan. Bake for 20-22 minutes, or until edges of shortbread are golden brown.
3. Meanwhile, in a large saucepan over medium heat melt ½ c. butter, condensed milk, corn syrup and brown sugar. Stir mixture constantly with a wooden spoon until mixture has thickened and is a deep caramel brown.
4. Pour caramel over freshly baked shortbread and spread it evenly in a thin layer with the back of a wooden spoon or a spatula. Place it in the fridge to set for 30 minutes.
5. Then, melt the chocolate chips in a bowl in the microwave until it forms a smooth and creamy chocolate sauce.
6. After 30 minutes, remove caramel from the fridge and spread the chocolate over top. Return to fridge to chill for an additional 30 minutes. Then, cut into squares or triangles and serve.