Gooey Chocolate Chip Sandwich Bars
from vanillasugarblog.com 
adapted from Food and Wine


Ingredients
2 cups AP flour
1 cup old fashioned rolled oats
1 tsp baking powder
1 tsp baking soda
1 tsp kosher salt
2 1/2 sticks unsalted butter, room temperature
1 cup light brown sugar
1/2 cup granulated sugar
1 large egg, room temperature
1 large egg yolk, room temperature
1 tbsp pure vanilla extract
3/4 cup semi-sweet chocolate chips
3/4 cup peanut butter chips
1 1/2 cups dried cranberries
2 cups semisweet chocolate chips
14-oz can sweetened condensed milk
2 tsp pure vanilla extract

Instructions
1. Preheat the oven to 350.  Lightly grease a 9x13-inch baking pan.  Line the dish with parchment paper leaving 1-inch of overhang on either side.
2. In a medium bowl, mix the flour with the oats, baking powder, baking soda and salt. In a stand mixer fitted with a paddle attachment, cream together the butter and sugars until light and fluffy.  
Add the egg, followed by the egg yolk and vanilla, scraping down the sides after each addition.  
Beat in the dry ingredients, then add 3/4 cup chocolate chips, peanut butter chips and dried cranberries until just incorporated.  Set aside.
3. In a small saucepan, melt 2 cups chocolate chips in the sweetened condensed milk over low heat, stirring constantly, until smooth and thickened, about 3 minutes.  Remove from the heat.  Stir in the vanilla and let cool to room temperature.
4. Press half the cookie dough into the prepared baking dish.  Pour the cooled chocolate mixture over the dough and spread evenly.  
Top with small dollops of the remaining cookie dough.  Bake for 20 to 25 minutes, until the top is lightly browned.  Let cool completely before cutting.