Butter Tart Cookie Bars

Instructions

PLEASE NOTE that procedure photos for this recipe appear above in the body of the post and below in the notes for easy reference.

To prepare the base layer

1. This recipe uses a 9x13 baking pan. In this recipe I think it is best to line to lightly grease the pan and line it with parchment paper so that you can lift the entire batch out of the pan after they have cooled and cut them on a cutting board. With cookie bars like this, which have different textures in the different layers, this enables you to have a more precise feeling for how to cut them well. More about that a little later in the recipe.
2. Preheat oven to 350 degrees F for aluminum bake ware and 325 degrees F for glass bake ware.
3. Mix together the 1/34 cups flour and ½ cup sugar.
4. Rub the butter through the flour mixture until it is well incorporated and resembles a dry coarse meal. (You can pulse the butter into the flour mixture using a food processor if you prefer.)
5. Press the crumb mixture firmly and evenly into the bottom of the prepared baking pan and bake for 10-12 minutes. The crumb mixture is normally quite crumbly but comes together in the baking.

To prepare the top layer

1. Whisk together all of the ingredients except the raisins until smooth. 
2. Let stand while the bottom layer bakes, then whisk again to make sure the brown sugar is completely dissolved into the mixture.
3. Pour onto the top of the baked base.
4. If using raisins, sprinkle them evenly over the surface of the topping in the pan.

To finish the cookie bars.

1. Return to the oven for an additional 25 minutes.
2. Remove from the oven and let them cool in the pan to room temperature.
3. As these cut better when cold, chill for a couple of hours or overnight in the fridge.
4. Cut into squares or bars and store in airtight containers in the fridge or freezer.
5. I lift the cookies from the pan after they have fully cooled in the fridge and lay them out on a cutting board. I've found the best thing to use is a sharp, long bladed knife held horizontally to push through the top layer before pushing on through to the crisp layer below. 
6. I cut one entire row of cookies off at a time and then cut each row separately into individual cookie bars.
7. These are quite rich, so although I cut the pan into 4 rows by 6 rows for 24 larger cookie squares for the recipe photos, you can easily cut the 4 rows into 9 cookie bars for a total of 36 cookie bars instead.