Dissolve the instant coffee into the espresso – completely
Pour the coffee mix over the chocolate in a glass bowl and heat in the microwave about 30 seconds and mix with a spatula until you have a smooth mixture
Transfer to a mixing bowl and allow it to cool until it’s just slightly warm, but not solidified
Mix with a paddle attachment on low speed, adding 2 tablespoons of softened butter at a time, then add the egg yolks and after they are integrated, add the powdered sugar
Mix until you have a smooth mixture and stop. Do not overmix
Fill a piping bag with a medium star tip and chill in the refrigerator while you make the Chantilly cream filling.
Notes
Make this when ready to make the chantilly cream filling and finish the Dacquoise. If it sets in the fridge too long it will set up too hard to pipe.