Ultimate Chocolate Sandwich Cookies

If you have ever even considered applying the word "chocoholic" to yourself, you simply must make these cookies. They are the ultimate in chocolate sandwich cookie-ness.
They start with fairly thin chocolate cookies that come out of the oven slightly crisp at the edges, due to their thickness (or lack thereof), and have a chewy, chocolaty center. The cookies are rather like thin brownies and have an intense taste that doesn't get overwhelming because they are thin. And they are loaded up with chocolate chunks of varying sizes, too.
The filling is basically the topping I used the other day to finish off a cinnamon cake. I added a bit of vanilla to it to round the flavor out ever so slightly. As it cools and solidifies, it melds with the outside cookies, producing an incredibly chocolaty treat that just cries out for a big glass of milk.

The cookies themselves are very easy to make and the only thing to keep in mind is that they will spread a lot. Use a teaspoon or a rounded teaspoon (yes, the actual measuring utensil) to divide up the dough. Try to chop the chocolate chunks relatively finely or use mini chocolate chips to get an even distribution of them.
Again, I can't really overstate the necessity of having a glass of milk nearby when you try one. You'll need it.

Ultimate Chocolate Sandwich Cookies
(cookies adapted from Epicurious)
1 cup all purpose flour
3 tbsp cocoa powder
1 tsp baking soda
1/2 tsp salt
1/2 cup butter, room temperature
2/3 cup brown sugar
1/4 cup sugar
1 large egg
2 tsp water
1 tsp vanilla extract
1 tsp instant coffee (or espresso) granules
1 1/2 cups mini chocolate chips or finely chunked bittersweet chocolate

Preheat oven to 325F. Line a baking sheet with parchment paper.
In a medium bowl, sift together the flour, cocoa, baking soda, and salt.
In a large bowl, cream together butter and both sugars until light. Beat in egg, water, vanilla and instant coffee powder. Gradually add in the flour mixture, using the mixer on low speed. Stir in chocolate chunks/mini chips. Drop dough by rounded teaspoonfuls the baking sheet, spacing about 2 inches apart.
Bake for about 12 minutes, until the cookies are slighly firm at the edges and no longer shiny in the center (baking time may be slightly shorter or longer depending on the exact size you scoop).
Cool on baking sheet for 5-10 minutes and then transfer to wire rack to cool.

Filling
6-oz bittersweet chocolate, finely chopped
2 1/2 tbsp butter, room temperature
1/2 tsp vanilla extract

Melt together the chocolate and the butter in a small glass bowl on low power in the microwave, checking and stirring every 20-30 seconds until it is smooth. Stir in vanilla extract. If the chocolate is runny, let it stand for a few minutes until it thickens and is spreadable.
Sandwich about 1 tsp (or as desired - I didn't measure and had two cookies left unfilled) between cookies.

Makes about 24 sandwich cookies.