Now, on to the butter creme. Put the butter, powdered sugar and coffee powder in the bowl and use your hand mixer to mix together. Start with the mixer on the slowest setting, to prevent dusting yourself and the entire kitchen. When the mixture is ready, prepare the piping bag. Important: the cookies need to be cool before you pipe on the butter creme to prevent it from melting.
Pipe on a narrow line of butter creme on the cookie’s flat side, the side that was on the baking sheet. Do not fill the cookie to the ends: it should not pour out when you press the cookies together. Place a second cookie on top, flat side on the butter creme, carefully press and set aside. Repeat for all the cookies.
Look at the result, and be proud of the result so far.
Fill a pan with hot water and place on your stove. Place a glass bowl on it, and make sure the bowl does not touch the water. Place 75% of the chocolate in the bowl and let is melt. Using the cooking thermometer, carefully monitor the temperature. When it hits 45°C/113°F, immediately take the bowl off the pan (make sure not to burn your hands) and stir in the remaining 25% of the chocolate chips. Keep stirring until all the chocolate has melted. Be careful not to allow any moisture to hit the chocolate: stay away from water.
Pick up a cookie, and dip the one end in the molten chocolate. Turn, and repeat for the other end. Place on a piece of parchment paper to cool. Repeat for all the cookies.
Put in the fridge to allow the chocolate to fully harden again.