For the Cookies:

1. Preheat the oven to 300°F and line a baking sheet with parchment paper. Set aside.
2. In a small bowl, combine the chocolate and the butter. Microwave on low for 1 minute, stopping and stirring the mixture every 15 seconds. Stir until completely melted and smooth. Set aside.
3. Whisk together the flour, baking powder, salt, cocoa powder, and instant espresso. Set aside.
4. Using a stand or hand-held mixer, beat the eggs, sugar, water, and vanilla on high until well combined and frothy.
5. Pour in the melted chocolate mixture and mix until it is thoroughly incorporated and the mixture is creamy and smooth.
6. Add the dry ingredients in batches, mixing after each addition. Fold in the mini chocolate chips.
7. Using a small ice cream or cookie scoop, scoop out the batter into roughly 1.5-inch balls and place on the prepared baking sheet. Bake for 18 minutes or until the cookies have puffed slightly and cracked. They will deflate slightly as they cool. Cool completely.

For the Filling:

1. While the cookies are baking, make the filling by beating the butter until light and fluffy. Add the powdered sugar and beat the mixture until incorporated.
2. Add the salt and caramel, tasting as you go, and mix until thoroughly combined. How much you add depends on your preference!

To Assemble:

1. Spread about 1 tablespoon of the filling on the flat side of a cookie and then top with another cookie, pushing down slightly. Continue until all cookie sandwiches are made.
2. Store in the fridge in an airtight container. I love these chilled, but if you do not, you can take them out of the fridge roughly 15 minutes before serving.