Preheat the oven to 400°F. Then line a jelly roll pan with aluminum foil and coat with non-stick cooking spray.
Cover the entire bottom of the pan with graham crackers. You may have to break some in half to completely cover the pan.
Add the butter and sugar in a medium saucepan. Melt over medium-low heat until the mixture begins to boil. Allow to boil for 2 minutes, stirring occasionally. Then remove from heat.
Add the sweetened condensed milk and stir for about 30 seconds to mix well. Let the toffee mixture cool for 1 minute.
Pour the mixture on top of the graham crackers. Use a spatula to spread in a thin layer over the crackers.
Place in oven and bake for 6-7 minutes or until you see the toffee mixture start to bubble.
Remove from oven and lay pan on a wire rack. Immediately sprinkle the white chocolate melts on top of the warm toffee graham crackers.
Once the graham crackers are completely covered with the white chocolate melts, use a spatula to spread the melted white chocolate evenly.
Before the white chocolate layer cools and sets, sprinkle with the dried cranberries (and blueberries if you use them).
Chill for 1 hour before cutting or breaking into pieces to serve.
You can store the graham cracker toffee in an airtight container for up to one week.